diff --git a/LDP/howto/docbook/NFS-HOWTO/NFS-HOWTO.sgml b/LDP/howto/docbook/NFS-HOWTO/NFS-HOWTO.sgml index 45e8962e..e3392f45 100644 --- a/LDP/howto/docbook/NFS-HOWTO/NFS-HOWTO.sgml +++ b/LDP/howto/docbook/NFS-HOWTO/NFS-HOWTO.sgml @@ -22,7 +22,7 @@ jade -t sgml -i html -d /usr/lib/sgml/stylesheets/ldp.dsl\#html ../nfs-howto.sgm Barr
- tavis@mahler.econ.columbia.edu + tavis dot barr at liu dot edu
@@ -31,7 +31,7 @@ jade -t sgml -i html -d /usr/lib/sgml/stylesheets/ldp.dsl\#html ../nfs-howto.sgm Langfeldt
- janl@linpro.no + janl at linpro dot no
@@ -40,7 +40,16 @@ jade -t sgml -i html -d /usr/lib/sgml/stylesheets/ldp.dsl\#html ../nfs-howto.sgm Vidal
- skvidal@phy.duke.edu + skvidal at phy dot duke dot edu +
+ + + + Tom + McNeal + +
+ trmcneal at attbi dot com
diff --git a/LDP/howto/docbook/NFS-HOWTO/client.sgml b/LDP/howto/docbook/NFS-HOWTO/client.sgml index 65e8d09f..339073a3 100644 --- a/LDP/howto/docbook/NFS-HOWTO/client.sgml +++ b/LDP/howto/docbook/NFS-HOWTO/client.sgml @@ -9,19 +9,24 @@ standard distributions do. If you are using a 2.2 or later kernel with the /proc filesystem you can check the latter by reading the file /proc/filesystems and making sure there is a line containing - nfs. If not, you will need to build (or download) a kernel that has - NFS support built in. + nfs. If not, typing insmod nfs may make it + magically appear if NFS has been compiled as a module; otherwise, + you will need to build (or download) a kernel that has + NFS support built in. In general, kernels that do not have NFS + compiled in will give a very specific error when the + mount command below is run. To begin using machine as an NFS client, you will need the portmapper running on that machine, and to use NFS file locking, you will - also need rpc.statd and rpc.lockd + also need rpc.statd and rpc.lockd running on both the client and the server. Most recent distributions start those services by default at boot time; if yours doesn't, see for information on how to start them up. - With portmapper, lockd, and statd running, you should now be able to + With portmap, lockd, + and statd running, you should now be able to mount the remote directory from your server just the way you mount a local hard drive, with the mount command. Continuing our example from the previous section, suppose our server above is called @@ -32,7 +37,9 @@ # mount master.foo.com:/home /mnt/home and the directory /home on master will appear as the directory - /mnt/home on slave1. + /mnt/home on slave1. (Note that + this assumes we have created the directory /mnt/home + as an empty mount point beforehand.) If this does not work, see the Troubleshooting section (). @@ -106,9 +113,10 @@ The program accessing a file on a NFS mounted file system will hang when the server crashes. The process cannot be interrupted or killed (except by a "sure kill") unless you also - specify intr. When the NFS server is back online the program will - continue undisturbed from where it was. We recommend using hard, - intr on all NFS mounted file systems. + specify intr. When the + NFS server is back online the program will + continue undisturbed from where it was. We recommend using + hard,intr on all NFS mounted file systems. diff --git a/LDP/howto/docbook/NFS-HOWTO/interop.sgml b/LDP/howto/docbook/NFS-HOWTO/interop.sgml index 9fa52cd6..a96cd132 100644 --- a/LDP/howto/docbook/NFS-HOWTO/interop.sgml +++ b/LDP/howto/docbook/NFS-HOWTO/interop.sgml @@ -53,8 +53,10 @@ - Version 4.3.2 of AIX requires that file systems be exported with - the insecure option, which causes NFS to listen to requests from + Version 4.3.2 of AIX, and possibly earlier versions as well, + requires that file systems be exported with + the insecure option, which + causes NFS to listen to requests from insecure ports (i.e., ports above 1024, to which non-root users can bind). Older versions of AIX do not seem to require this. @@ -63,12 +65,14 @@ AIX clients will default to mounting version 3 NFS over TCP. If your Linux server does not support this, then you may need - to specify vers=2 and/or proto=udp in your mount options. + to specify vers=2 and/or + proto=udp in your mount options. - Using netmasks in /etc/exports seems to sometimes cause clients + Using netmasks in /etc/exports + seems to sometimes cause clients to lose mounts when another client is reset. This can be fixed by listing out hosts explicitly. @@ -95,13 +99,15 @@ Linux servers and BSD clients Some versions of BSD may make requests to the server from insecure ports, - in which case you will need to export your volumes with the insecure - option. See the man page for exports(5) for more details. + in which case you will need to export your volumes with the + insecure + option. See the man page for exports(5) + for more details. - Compaq Tru64 Unix + Tru64 Unix Tru64 Unix Servers and Linux Clients @@ -117,6 +123,12 @@ -root=slave1.foo.com:slave2.foo.com + + (The root option is listed in the last + entry for informational purposes only; its use is not recommended + unless necessary.) + + Tru64 checks the /etc/exports file every time there is a mount request so you do not need to run the exportfs command; in fact on many @@ -129,7 +141,8 @@ There are two issues to watch out for here. First, Tru64 Unix mounts using Version 3 NFS by default. You will see mount errors if your Linux server does not support Version 3 NFS. Second, in Tru64 Unix - 4.x, NFS locking requests are made by daemon. You will therefore + 4.x, NFS locking requests are made by + daemon. You will therefore need to specify the insecure_locks option on all volumes you export to a Tru64 Unix 4.x client; see the exports man pages for details. @@ -153,7 +166,9 @@ Linux Servers and HP-UX Clients HP-UX diskless clients will require at least a kernel version 2.2.19 - (or patched 2.2.18) for device files to export correctly. + (or patched 2.2.18) for device files to export correctly. Also, any + exports to an HP-UX client will need to be exported with the + insecure_locks option. @@ -176,11 +191,112 @@ 2.4 kernel. As a workaround, you can export and mount lower-down file systems separately. - + + As of Kernel 2.4.17, there continue to be several minor interoperability + issues that may require a kernel upgrade. In particular: + + + + Make sure that Trond Myklebust's seekdir + (or dir) kernel patch is applied. + The latest version (for 2.4.17) is located at: + + + + http://www.fys.uio.no/~trondmy/src/2.4.17/linux-2.4.17-seekdir.dif + + + + + IRIX servers do not always use the same + fsid attribute field across + reboots, which results in inode number mismatch + errors on a Linux + client if the mounted IRIX server reboots. A patch is available from: + + + http://www.geocrawler.com/lists/3/SourceForge/789/0/7777454/ + + + + + Linux kernels v2.4.9 and above have problems reading large directories + (hundreds of files) from exported IRIX XFS file systems that were made + with naming version=1. + The reason for the problem can be found at: + + + + http://www.geocrawler.com/archives/3/789/2001/9/100/6531172/ + + + The naming version can be found by using (on the IRIX server): + + + xfs_growfs -n mount_point + + + The workaround is to export these file systems using the + -32bitclients + option in the /etc/exports file. + The fix is to convert the file system to 'naming version=2'. + Unfortunately the only way to do this is by a + backup/mkfs/restore. + + + mkfs_xfs on IRIX 6.5.14 (and above) + creates naming version=2 XFS file + systems by default. On IRIX 6.5.5 to 6.5.13, use: + + mkfs_xfs -n version=2 device + + + + Versions of IRIX prior to 6.5.5 do not support + naming version=2 XFS file systems. + + + + + + + IRIX clients and Linux servers - There are no known interoperability issues. + Irix versions up to 6.5.12 have problems mounting file systems exported + from Linux boxes - the mount point "gets lost," e.g., + + # mount linux:/disk1 /mnt + # cd /mnt/xyz/abc + # pwd + /xyz/abc + + + + This is known IRIX bug (SGI bug 815265 - IRIX not liking file handles of + less than 32 bytes), which is fixed in IRIX 6.5.13. + If it is not possible + to upgrade to IRIX 6.5.13, then the unofficial + workaround is to force the Linux nfsd + to always use 32 byte file handles. + + + A number of patches exist - see: + + + + + http://www.geocrawler.com/archives/3/789/2001/8/50/6371896/ + + + + + + http://oss.sgi.com/projects/xfs/mail_archive/0110/msg00006.html + + + @@ -190,10 +306,11 @@ Solaris Servers Solaris has a slightly different format on the server end from - other operating systems. Instead of /etc/exports, the configuration - file is /etc/dfs/dfstab. Entries are of the form of a "share" - command, where the syntax for the example in would - look like + other operating systems. Instead of + /etc/exports, the configuration + file is /etc/dfs/dfstab. Entries are of + the form of a share command, where the syntax + for the example in would look like share -o rw=slave1,slave2 -d "Master Usr" /usr @@ -202,11 +319,13 @@ share -o rw=slave1,slave2 -d "Master Usr" /usr Solaris servers are especially sensitive to packet size. If you are using a Linux client with a Solaris server, be sure to set - rsize and wsize to 32768 at mount time. + rsize and wsize + to 32768 at mount time. Finally, there is an issue with root squashing on Solaris: root gets - mapped to the user noone, which is not the same as the user nobody. + mapped to the user noone, which + is not the same as the user nobody. If you are having trouble with file permissions as root on the client machine, be sure to check that the mapping works as you expect. @@ -221,7 +340,7 @@ svc: unknown program 100227 (me 100003) This happens because Solaris clients, when they mount, try to obtain - ACL information - which linux obviously does not have. The messages + ACL information - which Linux obviously does not have. The messages can safely be ignored. @@ -249,11 +368,16 @@ svc: unknown program 100227 (me 100003) /home -rw=slave1.foo.com,slave2.foo.com, root=slave1.foo.com,slave2.foo.com + + Again, the root option is listed for informational + purposes and is not recommended unless necessary. + SunOS Clients - Be advised that SunOS makes all NFS locking requests as daemon, and + Be advised that SunOS makes all NFS locking requests + as daemon, and therefore you will need to add the insecure_locks option to any volumes you export to a SunOS machine. See the exports man page for details. diff --git a/LDP/howto/docbook/NFS-HOWTO/intro.sgml b/LDP/howto/docbook/NFS-HOWTO/intro.sgml index 7a7156b3..faf57279 100644 --- a/LDP/howto/docbook/NFS-HOWTO/intro.sgml +++ b/LDP/howto/docbook/NFS-HOWTO/intro.sgml @@ -17,7 +17,8 @@ There are other systems that provide similar functionality to NFS. - Samba provides file services to Windows clients. The Andrew File + Samba (http://www.samba.org) + provides file services to Windows clients. The Andrew File System from IBM (http://www.transarc.com/Product/EFS/AFS/index.html), recently open-sourced, provides a file sharing mechanism with some additional security and performance features. The Coda File System @@ -42,10 +43,8 @@ This HOWTO is not a description of the guts and underlying structure of NFS. For that you may wish to read - Managing NFS and NIS by Hal Stern, published by O'Reilly & - Associates, Inc. While that book is severely out of date, much - of the structure of NFS has not changed, and the book describes it - very articulately. A much more advanced and up-to-date technical + Linux NFS and Automounter Administration by Erez Zadok (Sybex, 2001). The classic NFS book, updated and still quite useful, is Managing NFS and NIS by Hal Stern, published by O'Reilly & + Associates, Inc. A much more advanced technical description of NFS is available in NFS Illustrated by Brent Callaghan. @@ -58,7 +57,7 @@ It will also not cover PC-NFS, which is considered obsolete (users - are encouraged to use Samba to share files with PC's) or NFS + are encouraged to use Samba to share files with Windows machines) or NFS Version 4, which is still in development. @@ -98,7 +97,8 @@ patches have been added because NFS Version 3 server support will be a configuration option. However, unless you have some particular reason to use an older kernel, you should upgrade because many bugs - have been fixed along the way. + have been fixed along the way. Kernel 2.2.19 contains some additional + locking improvements over 2.2.18. Version 3 functionality will also require the nfs-utils package of @@ -111,11 +111,24 @@ All 2.4 and higher kernels have full NFS Version 3 functionality. + + In all cases, if you are building your own kernel, you will need + to select NFS and NFS Version 3 support at compile time. Most + (but not all) standard distributions come with kernels that support + NFS version 3. + + + Handling files larger than 2 GB will require a 2.4x kernel and a + 2.2.x version of glibc. + All kernels after 2.2.18 support NFS over TCP on the client side. - As of this writing, server-side NFS over TCP only exists in the - later 2.2 series (but not yet in the 2.4 kernels), is considered - experimental, and is somewhat buggy. + As of this writing, server-side NFS over TCP only exists in a + buggy form as an experimental option in the post-2.2.18 series; + patches for 2.4 and 2.5 kernels have been introduced starting with + 2.4.17 and 2.5.6. The patches are believed to be stable, though + as of this writing they are relatively new and have not seen + widespread use or integration into the mainstream 2.4 kernel. Because so many of the above functionalities were introduced in @@ -125,8 +138,9 @@ correctly. - As we write this document, NFS version 4 is still in development - as a protocol, and it will not be dealt with here. + As we write this document, NFS version 4 has only recently been + finalized as a protocol, and no implementations are considered + production-ready. It will not be dealt with here. @@ -137,7 +151,66 @@ mailing lists as well as the latest version of nfs-utils, NFS kernel patches, and other NFS related packages. - + + +When you encounter a problem or have a question not covered in this +manual, the faq or the man pages, you should send a message to the nfs +mailing list (nfs@lists.sourceforge.net). To best help the developers +and other users help you assess your problem you should include: + + + + + the version of nfs-utils you are using + + + + the version of the kernel and any non-stock applied kernels. + + + + + the distribution of linux you are using + + + + + the version(s) of other operating systems involved. + + + + +It is also useful to know the networking configuration connecting the +hosts. + + +If your problem involves the inability mount or export shares please +also include: + + + + + a copy of your /etc/exports file + + + + + the output of rpcinfo -p localhost run on the server + + + + + the output of rpcinfo -p servername run on the client + + + + +Sending all of this information with a specific question, after reading +all the documentation, is the best way to ensure a helpful response from +the list. + + You may also wish to look at the man pages for nfs(5), exports(5), mount(8), fstab(5), nfsd(8), lockd(8), statd(8), diff --git a/LDP/howto/docbook/NFS-HOWTO/performance.sgml b/LDP/howto/docbook/NFS-HOWTO/performance.sgml index 72a4434a..db2e0111 100644 --- a/LDP/howto/docbook/NFS-HOWTO/performance.sgml +++ b/LDP/howto/docbook/NFS-HOWTO/performance.sgml @@ -1,252 +1,652 @@ Optimizing NFS Performance - Getting network settings right can improve NFS performance many times - over -- a tenfold increase in transfer speeds is not unheard of. - The most important things to get right are the rsize - and wsize mount options. Other factors listed below - may affect people with particular hardware setups. - +Careful analysis of your environment, both from the client and from the server +point of view, is the first step necessary for optimal NFS performance. The +first sections will address issues that are generally important to the client. +Later ( and beyond), server side issues +will be discussed. In both +cases, these issues will not be limited exclusively to one side or the other, +but it is useful to separate the two in order to get a clearer picture of +cause and effect. + + +Aside from the general network configuration - appropriate network capacity, +faster NICs, full duplex settings in order to reduce collisions, agreement in +network speed among the switches and hubs, etc. - one of the most important +client optimization settings are the NFS data transfer buffer sizes, specified +by the mount command options rsize +and wsize. + Setting Block Size to Optimize Transfer Speeds - The rsize and wsize - mount options specify the size of the chunks of data - that the client and server pass back and forth to each other. If no - rsize and wsize options - are specified, the default varies by which version of NFS we are using. - 4096 bytes is the most common default, although for TCP-based mounts - in 2.2 kernels, and for all mounts beginning with 2.4 kernels, the - server specifies the default block size. - - - The defaults may be too big or too small. On the one hand, some - combinations of Linux kernels and network cards (largely on older - machines) cannot handle blocks that large. On the other hand, if they - can handle larger blocks, a bigger size might be faster. - - - So we'll want to experiment and find an rsize and wsize that works - and is as fast as possible. You can test the speed of your options - with some simple commands. - - - The first of these commands transfers 16384 blocks of 16k each from - the special file /dev/zero (which if you read it - just spits out zeros _really_ fast) to the mounted partition. We will - time it to see how long it takes. So, from the client machine, type: - +The mount command options rsize +and wsize specify the size of the chunks of +data that the client and server pass back and forth +to each other. If no rsize +and wsize options are specified, +the default varies by which version of NFS we +are using. The most common default is 4K (4096 bytes), although for TCP-based +mounts in 2.2 kernels, and for all mounts beginning with 2.4 kernels, the +server specifies the default block size. + + +The theoretical limit for the NFS V2 protocol is 8K. For the V3 protocol, the +limit is specific to the server. On the Linux server, the maximum block size +is defined by the value of the kernel constant +NFSSVC_MAXBLKSIZE, found in the +Linux kernel source file ./include/linux/nfsd/const.h. +The current maximum block size for the kernel, as of 2.4.17, is 8K (8192 bytes), +but the patch set implementing NFS over TCP/IP transport in the 2.4 +series, as of this writing, uses a value of 32K (defined in the +patch as 32*1024) for the maximum block size. + + +All 2.4 clients currently support up to 32K block transfer sizes, allowing the +standard 32K block transfers across NFS mounts from other servers, such as +Solaris, without client modification. + + +The defaults may be too big or too small, depending on the specific +combination of hardware and kernels. On the one hand, some combinations of +Linux kernels and network cards (largely on older machines) cannot handle +blocks that large. On the other hand, if they can handle larger blocks, a +bigger size might be faster. + + +You will want to experiment and find an rsize +and wsize that works and is as +fast as possible. You can test the speed of your options with some simple +commands, if your network environment is not heavily used. Note that your +results may vary widely unless you resort to using more complex benchmarks, +such as Bonnie, Bonnie++, +or IOzone. + + +The first of these commands transfers 16384 blocks of 16k each from the +special file /dev/zero (which if +you read it just spits out zeros really +fast) to the mounted partition. We will time it to see how long it takes. So, +from the client machine, type: + + # time dd if=/dev/zero of=/mnt/home/testfile bs=16k count=16384 - - - - This creates a 256Mb file of zeroed bytes. In general, you should - create a file that's at least twice as large as the system RAM - on the server, but make sure you have enough disk space! Then read - back the file into the great black hole on the client machine - (/dev/null) by typing the following: - + + +This creates a 256Mb file of zeroed bytes. In general, you should create a +file that's at least twice as large as the system RAM on the server, but make +sure you have enough disk space! Then read back the file into the great black +hole on the client machine (/dev/null) by +typing the following: + + # time dd if=/mnt/home/testfile of=/dev/null bs=16k - - - - Repeat this a few times and average how long it takes. Be sure to - unmount and remount the filesystem each time (both on the client and, - if you are zealous, locally on the server as well), which should clear - out any caches. - - - Then unmount, and mount again with a larger and smaller block size. - They should probably be multiples of 1024, and not larger than - 8192 bytes since that's the maximum size in NFS version 2. (Though - if you are using Version 3 you might want to try up to 32768.) - Wisdom has it that the block size should be a power of two since most - of the parameters that would constrain it (such as file system block - sizes and network packet size) are also powers of two. However, some - users have reported better successes with block sizes that are not - powers of two but are still multiples of the file system block size - and the network packet size. - - - Directly after mounting with a larger size, cd into the mounted - file system and do things like ls, explore the fs a bit to make - sure everything is as it should. If the rsize/wsize is too large - the symptoms are very odd and not 100% obvious. A typical symptom - is incomplete file lists when doing 'ls', and no error messages. - Or reading files failing mysteriously with no error messages. After - establishing that the given rsize/wsize works you can do the speed - tests again. Different server platforms are likely to have different - optimal sizes. SunOS and Solaris is reputedly a lot faster with 4096 - byte blocks than with anything else. - - - Remember to edit /etc/fstab to reflect the rsize/wsize you found. - + + +Repeat this a few times and average how long it takes. Be sure to unmount and +remount the filesystem each time (both on the client and, if you are zealous, +locally on the server as well), which should clear out any caches. + + +Then unmount, and mount again with a larger and smaller block size. They +should be multiples of 1024, and not larger than the maximum block size +allowed by your system. Note that NFS Version 2 is limited to a maximum of 8K, +regardless of the maximum block size defined by +NFSSVC_MAXBLKSIZE; Version 3 +will support up to 64K, if permitted. The block size should be a power of two +since most of the parameters that would constrain it (such as file system +block sizes and network packet size) are also powers of two. However, some +users have reported better successes with block sizes that are not powers of +two but are still multiples of the file system block size and the network +packet size. + + +Directly after mounting with a larger size, cd into the mounted +file system and do things like ls, explore +the filesystem a bit to make sure everything is as it +should. If the rsize/wsize + is too large the symptoms are very odd and not 100% +obvious. A typical symptom is incomplete file lists when doing +ls, and no +error messages, or reading files failing mysteriously with no error messages. +After establishing that the given rsize/ +wsize works you can do the speed tests +again. Different server platforms are likely to have different optimal sizes. + + +Remember to edit /etc/fstab to reflect the +rsize/wsize you found +to be the most desirable. + + +If your results seem inconsistent, or doubtful, you may need to analyze your +network more extensively while varying the rsize +and wsize values. In that +case, here are several pointers to benchmarks that may prove useful: + + + + + Bonnie http://www.textuality.com/bonnie/ + + + + + Bonnie++ http://www.coker.com.au/bonnie++/ + + + + + IOzone file system benchmark http://www.iozone.org/ + + + + + The official NFS benchmark, + SPECsfs97 http://www.spec.org/osg/sfs97/ + + + + +The easiest benchmark with the widest coverage, including an extensive spread +of file sizes, and of IO types - reads, & writes, rereads & rewrites, random +access, etc. - seems to be IOzone. A recommended invocation of IOzone (for +which you must have root privileges) includes unmounting and remounting the +directory under test, in order to clear out the caches between tests, and +including the file close time in the measurements. Assuming you've already +exported /tmp to everyone from the server +foo, +and that you've installed IOzone in the local directory, this should work: + + + # echo "foo:/tmp /mnt/foo nfs rw,hard,intr,rsize=8192,wsize=8192 0 0" + >> /etc/fstab + # mkdir /mnt/foo + # mount /mnt/foo + # ./iozone -a -R -c -U /mnt/foo -f /mnt/foo/testfile > logfile + + +The benchmark should take 2-3 hours at most, but of course you will need to +run it for each value of rsize and wsize that is of interest. The web site +gives full documentation of the parameters, but the specific options used +above are: + + + + + -a Full automatic mode, which tests file sizes of 64K to 512M, using + record sizes of 4K to 16M + + + + + -R Generate report in excel spreadsheet form (The "surface plot" + option for graphs is best) + + + + + -c Include the file close time in the tests, which will pick up the + NFS version 3 commit time + + + + + -U Use the given mount point to unmount and remount between tests; + it clears out caches + + + + + -f When using unmount, you have to locate the test file in the + mounted file system + + + Packet Size and Network Drivers - There are many shoddy network drivers available for Linux, - including for some fairly standard cards. - + While many Linux network card drivers are excellent, some are quite shoddy, + including a few drivers for some fairly standard cards. It is worth + experimenting with your network card directly to find out how it can + best handle traffic. + + + Try pinging back and forth + between the two machines with large packets using + the -f and -s + options with ping (see ping(8) + for more details) and see if a + lot of packets get dropped, or if they take a long time for a reply. If so, + you may have a problem with the performance of your network card. + + +For a more extensive analysis of NFS behavior in particular, use the +nfsstat command to look at nfs transactions, client and server statistics, network +statistics, and so forth. The "-o net" option will show you the number of +dropped packets in relation to the total number of transactions. In UDP +transactions, the most important statistic is the number of retransmissions, +due to dropped packets, socket buffer overflows, general server congestion, +timeouts, etc. This will have a tremendously important effect on NFS +performance, and should be carefully monitored. +Note that nfsstat does not yet +implement the -z option, which would zero out all counters, so you must look +at the current nfsstat counter values prior to running the benchmarks. + + +To correct network problems, you may wish to reconfigure the packet size that +your network card uses. Very often there is a constraint somewhere else in the +network (such as a router) that causes a smaller maximum packet size between +two machines than what the network cards on the machines are actually capable +of. TCP should autodiscover the appropriate packet size for a network, but UDP +will simply stay at a default value. So determining the appropriate packet +size is especially important if you are using NFS over UDP. + + +You can test for the network packet size using the tracepath command: From +the client machine, just type tracepath +server 2049 and the path MTU should +be reported at the bottom. You can then set the MTU on your network card equal +to the path MTU, by using the MTU +option to ifconfig, and see if fewer packets +get dropped. See the ifconfig man pages for details on how to reset the MTU. + + +In addition, netstat -s will give the statistics collected for traffic across +all supported protocols. You may also look at +/proc/net/snmp for information +about current network behavior; see the next section for more details. + + + + Overflow of Fragmented Packets - Try pinging back and forth between the two machines with large - packets using the and - options with ping (see man ping) - for more details and see if a lot of packets get or if they - take a long time for a reply. If so, you may have a problem - with the performance of your network card. - +Using an rsize or wsize +larger than your network's MTU (often set to 1500, in +many networks) will cause IP packet fragmentation when using NFS over UDP. IP +packet fragmentation and reassembly require a significant amount of CPU +resource at both ends of a network connection. In addition, packet +fragmentation also exposes your network traffic to greater unreliability, +since a complete RPC request must be retransmitted if a UDP packet fragment is +dropped for any reason. Any increase of RPC retransmissions, along with the +possibility of increased timeouts, are the single worst impediment to +performance for NFS over UDP. + + +Packets may be dropped for many reasons. If your network topography is +complex, fragment routes may differ, and may not all arrive at the Server for +reassembly. NFS Server capacity may also be an issue, since the kernel has a +limit of how many fragments it can buffer before it starts throwing away +packets. With kernels that support the /proc +filesystem, you can monitor the +files /proc/sys/net/ipv4/ipfrag_high_thresh and +/proc/sys/net/ipv4/ipfrag_low_thresh. Once the number of unprocessed, +fragmented packets reaches the number specified by ipfrag_high_thresh (in +bytes), the kernel will simply start throwing away fragmented packets until +the number of incomplete packets reaches the number specified by +ipfrag_low_thresh. + + +Another counter to monitor is IP: ReasmFails +in the file /proc/net/snmp; this +is the number of fragment reassembly failures. if it goes up too quickly +during heavy file activity, you may have problem. + + + + NFS over TCP - To correct such a problem, you may wish to reconfigure the packet - size that your network card uses. Very often there is a constraint - somewhere else in the network (such as a router) that causes a - smaller maximum packet size between two machines than what the - network cards on the machines are actually capable of. TCP should - autodiscover the appropriate packet size for a network, but UDP - will simply stay at a default value. So determining the appropriate - packet size is especially important if you are using NFS over UDP. - +A new feature, available for both 2.4 and 2.5 kernels but not yet +integrated into the mainstream kernel at the time of +this writing, is NFS over TCP. Using TCP +has a distinct advantage and a distinct disadvantage over UDP. The advantage +is that it works far better than UDP on lossy networks. +When using TCP, a single dropped packet can be retransmitted, without +the retransmission of the entire RPC request, resulting in better performance +on lossy networks. In addition, TCP will handle network speed differences +better than UDP, due to the underlying flow control at the network level. + + +The disadvantage of using TCP is that it is not a stateless protocol like +UDP. If your server crashes in the middle of a packet transmission, +the client will hang and any shares will need to be unmounted and remounted. + + +The overhead incurred by the TCP protocol will result in +somewhat slower performance than UDP under ideal network +conditions, but the cost is not severe, and is often not +noticable without careful measurement. If you are using +gigabit ethernet from end to end, you might also investigate the +usage of jumbo frames, since the high speed network may +allow the larger frame sizes without encountering increased +collision rates, particularly if you have set the network +to full duplex. + + + + Timeout and Retransmission Values - You can test for the network packet size using the tracepath command: - From the client machine, just type tracepath [server] 2049 - and the path MTU should be reported at the bottom. You can then set the - MTU on your network card equal to the path MTU, by using the MTU option - to ifconfig, and see if fewer packets get dropped. - See the ifconfig man pages for details on how to reset the MTU. - +Two mount command options, timeo +and retrans, control the behavior of UDP +requests when encountering client timeouts due to dropped packets, network +congestion, and so forth. The -o timeo +option allows designation of the length +of time, in tenths of seconds, that the client will wait until it decides it +will not get a reply from the server, and must try to send the request again. +The default value is 7 tenths of a second. The +-o retrans option allows +designation of the number of timeouts allowed before the client gives up, and +displays the Server not responding +message. The default value is 3 attempts. +Once the client displays this message, it will continue to try to send +the request, but only once before displaying the error message if +another timeout occurs. When the client reestablishes contact, it +will fall back to using the correct retrans +value, and will display the Server OK message. + + +If you are already encountering excessive retransmissions (see the output of +the nfsstat command), or want to increase the block transfer size without +encountering timeouts and retransmissions, you may want to adjust these +values. The specific adjustment will depend upon your environment, and in most +cases, the current defaults are appropriate. + - Number of Instances of NFSD + Number of Instances of the NFSD Server Daemon - Most startup scripts, Linux and otherwise, start 8 instances of nfsd. - In the early days of NFS, Sun decided on this number as a rule of thumb, - and everyone else copied. There are no good measures of how many - instances are optimal, but a more heavily-trafficked server may require - more. If you are using a 2.4 or higher kernel and you want to see how - heavily each nfsd thread is being used, you can look at the file - /proc/net/rpc/nfsd. The last ten numbers on the - th line in that file indicate the number of seconds - that the thread usage was at that percentage of the maximum allowable. - If you have a large number in the top three deciles, you may wish to - increase the number of nfsd instances. This is done - upon starting nfsd using the number of instances as - the command line option. See the nfsd man page for - more information. - +Most startup scripts, Linux and otherwise, start 8 instances of +nfsd. In the +early days of NFS, Sun decided on this number as a rule of thumb, and everyone +else copied. There are no good measures of how many instances are optimal, but +a more heavily-trafficked server may require more. +You should use at the very least one daemon per processor, but +four to eight per processor may be a better rule of thumb. +If you are using a 2.4 or +higher kernel and you want to see how heavily each +nfsd thread is being used, +you can look at the file /proc/net/rpc/nfsd. +The last ten numbers on the th +line in that file indicate the number of seconds that the thread usage was at +that percentage of the maximum allowable. If you have a large number in the +top three deciles, you may wish to increase the number +of nfsd instances. This +is done upon starting nfsd using the +number of instances as the command line +option, and is specified in the NFS startup script +(/etc/rc.d/init.d/nfs on +Red Hat) as RPCNFSDCOUNT. +See the nfsd(8) man page for more information. + Memory Limits on the Input Queue - On 2.2 and 2.4 kernels, the socket input queue, where requests - sit while they are currently being processed, has a small default - size limit of 64k. This means that if you are running 8 instances of - nfsd, each will only have 8k to store requests while it processes - them. - - - You should consider increasing this number to at least 256k for nfsd. - This limit is set in the proc file system using the files - /proc/sys/net/core/rmem_default and /proc/sys/net/core/rmem_max. - It can be increased in three steps; the following method is a bit of - a hack but should work and should not cause any problems: - - - - - Increase the size listed in the file: - - echo 262144 > /proc/sys/net/core/rmem_default - echo 262144 > /proc/sys/net/core/rmem_max - - - - - - Restart nfsd, e.g., type /etc/rc.d/init.d/nfsd restart on Red Hat - - - - - Return the size limits to their normal size in case other kernel systems depend on it: - - echo 65536 > /proc/sys/net/core/rmem_default - echo 65536 > /proc/sys/net/core/rmem_max - - - - - Be sure to perform this last step because machines have been reported - to crash if these values are left changed for long periods of time. - - - - +On 2.2 and 2.4 kernels, the socket input queue, where requests sit while they +are currently being processed, has a small default size limit (rmem_default) +of 64k. This queue is important for clients with heavy read loads, and servers +with heavy write loads. As an example, if you are running 8 instances of nfsd +on the server, each will only have 8k to store write requests while it +processes them. In addition, the socket output queue - important for clients +with heavy write loads and servers with heavy read loads - also has a small +default size (wmem_default). + + +Several published runs of the NFS benchmark +SPECsfs +specify usage of a much higher value for both +the read and write value sets, [rw]mem_default and +[rw]mem_max. You might +consider increasing these values to at least 256k. The read and write limits +are set in the proc file system using (for example) the files +/proc/sys/net/core/rmem_default and +/proc/sys/net/core/rmem_max. The +rmem_default value can be increased in three steps; the following method is a +bit of a hack but should work and should not cause any problems: + + + + + Increase the size listed in the file: + + + # echo 262144 > /proc/sys/net/core/rmem_default + # echo 262144 > /proc/sys/net/core/rmem_max + + + + + Restart NFS. For example, on Red Hat systems, + + + # /etc/rc.d/init.d/nfs restart + + + + + You might return the size limits to their normal size in case other + kernel systems depend on it: + + + # echo 65536 > /proc/sys/net/core/rmem_default + # echo 65536 > /proc/sys/net/core/rmem_max + + + + + This last step may be necessary because machines have been reported to + crash if these values are left changed for long periods of time. - - - - Overflow of Fragmented Packets - - The NFS protocol uses fragmented UDP packets. The kernel has - a limit of how many fragments of incomplete packets it can - buffer before it starts throwing away packets. With 2.2 kernels - that support the /proc filesystem, you can - specify how many by editing the files - /proc/sys/net/ipv4/ipfrag_high_thresh and - /proc/sys/net/ipv4/ipfrag_low_thresh. - - - Once the number of unprocessed, fragmented packets reaches the - number specified by ipfrag_high_thresh (in bytes), the kernel - will simply start throwing away fragmented packets until the number - of incomplete packets reaches the number specified - by ipfrag_low_thresh. (With 2.2 kernels, the default is usually 256K). - This will look like packet loss, and if the high threshold is - reached your server performance drops a lot. - - - One way to monitor this is to look at the field IP: ReasmFails in the - file /proc/net/snmp; if it goes up too quickly during heavy file - activity, you may have problem. Good alternative values for - ipfrag_high_thresh and ipfrag_low_thresh - have not been reported; if you have a good experience with a - particular value, please let the maintainers and development team know. - Turning Off Autonegotiation of NICs and Hubs - Sometimes network cards will auto-negotiate badly with - hubs and switches and this can have strange effects. - Moreover, hubs may lose packets if they have different - ports running at different speeds. Try playing around - with the network speed and duplex settings. - +If network cards auto-negotiate badly with hubs and switches, and ports run at +different speeds, or with different duplex configurations, performance will be +severely impacted due to excessive collisions, dropped packets, etc. If you +see excessive numbers of dropped packets in the +nfsstat output, or poor +network performance in general, try playing around with the network speed and +duplex settings. If possible, concentrate on establishing a 100BaseT full +duplex subnet; the virtual elimination of collisions in full duplex will +remove the most severe performance inhibitor for NFS over UDP. Be careful +when turning off autonegotiation on a card: The hub or switch that the card +is attached to will then resort to other mechanisms (such as parallel detection) +to determine the duplex settings, and some cards default to half duplex +because it is more likely to be supported by an old hub. The best solution, +if the driver supports it, is to force the card to negotiate 100BaseT +full duplex. + + + + Synchronous vs. Asynchronous Behavior in NFS + +The default export behavior for both NFS Version 2 and Version 3 protocols, +used by exportfs in nfs-utils +versions prior to Version 1.11 (the latter is in the CVS tree, +but not yet released in a package, as of January, 2002) is +"asynchronous". This default permits the server to reply to client requests as +soon as it has processed the request and handed it off to the local file +system, without waiting for the data to be written to stable storage. This is +indicated by the async option denoted in the server's export list. It yields +better performance at the cost of possible data corruption if the server +reboots while still holding unwritten data and/or metadata in its caches. This +possible data corruption is not detectable at the time of occurrence, since +the async option instructs the server to lie to the client, telling the +client that all data has indeed been written to the stable storage, regardless +of the protocol used. + + +In order to conform with "synchronous" behavior, used as the default for most +proprietary systems supporting NFS (Solaris, HP-UX, RS/6000, etc.), and now +used as the default in the latest version of exportfs, the Linux Server's +file system must be exported with the sync option. Note that specifying +synchronous exports will result in no option being seen in the server's export +list: + + + + + Export a couple file systems to everyone, using slightly different + options: + + + + # /usr/sbin/exportfs -o rw,sync *:/usr/local + # /usr/sbin/exportfs -o rw *:/tmp + + + + + + Now we can see what the exported file system parameters look like: + + + + # /usr/sbin/exportfs -v + /usr/local *(rw) + /tmp *(rw,async) + + + + + +If your kernel is compiled with the /proc filesystem, +then the file /proc/fs/nfs/exports will also show the +full list of export options. + + +When synchronous behavior is specified, the server will not complete (that is, +reply to the client) an NFS version 2 protocol request until the local file +system has written all data/metadata to the disk. The server +will complete a +synchronous NFS version 3 request without this delay, and will return the +status of the data in order to inform the client as to what data should be +maintained in its caches, and what data is safe to discard. There are 3 +possible status values, defined an enumerated type, nfs3_stable_how, in +include/linux/nfs.h. The values, along with the subsequent actions taken due +to these results, are as follows: + + + + +NFS_UNSTABLE - Data/Metadata was not committed to stable storage on the +server, and must be cached on the client until a subsequent client commit +request assures that the server does send data to stable storage. + + + + +NFS_DATA_SYNC - Metadata was not sent to stable storage, and must be cached +on the client. A subsequent commit is necessary, as is required above. + + + + +NFS_FILE_SYNC - No data/metadata need be cached, and a subsequent commit +need not be sent for the range covered by this request. + + + + +In addition to the above definition of synchronous behavior, the client may +explicitly insist on total synchronous behavior, regardless of the protocol, +by opening all files with the O_SYNC option. In this case, all replies to +client requests will wait until the data has hit the server's disk, regardless +of the protocol used (meaning that, in NFS version 3, all requests will be +NFS_FILE_SYNC requests, and will require that the Server returns this status). +In that case, the performance of NFS Version 2 and NFS Version 3 will be +virtually identical. + + +If, however, the old default async +behavior is used, the O_SYNC option has +no effect at all in either version of NFS, since the server will reply to the +client without waiting for the write to complete. In that case the performance +differences between versions will also disappear. + + +Finally, note that, for NFS version 3 protocol requests, a subsequent commit +request from the NFS client at file close time, or at fsync() time, will force +the server to write any previously unwritten data/metadata to the disk, and +the server will not reply to the client until this has been completed, as long +as sync behavior is followed. If async is used, the commit is essentially +a no-op, since the server once again lies to the client, telling the client that +the data has been sent to stable storage. This again exposes the client and +server to data corruption, since cached data may be discarded on the client +due to its belief that the server now has the data maintained in stable +storage. + Non-NFS-Related Means of Enhancing Server Performance - Offering general guidelines for setting up a well-functioning - file server is outside the scope of this document, but a few - hints may be worth mentioning: First, RAID 5 gives you good - read speeds but lousy write speeds; consider RAID 1/0 if both - write speed and redundancy are important. Second, using a - journalling filesystem will drastically reduce your reboot - time in the event of a system crash; as of this writing, ext3 - (ftp://ftp.uk.linux.org/pub/linux/sct/fs/jfs/) was the only - journalling filesystem that worked correctly with - NFS version 3, but no doubt that will change soon. - In particular, it looks like Reiserfs - should work with NFS version 3 on 2.4 kernels, though not yet - on 2.2 kernels. Finally, using an automounter (such as autofs - or amd) may prevent hangs if you cross-mount files - on your machines (whether on purpose or by oversight) and one of those - machines goes down. See the - Automount Mini-HOWTO - for details. - +In general, server performance and server disk access speed will have an +important effect on NFS performance. +Offering general guidelines for setting up a well-functioning file server is +outside the scope of this document, but a few hints may be worth mentioning: + + + + +If you have access to RAID arrays, use RAID 1/0 for both write speed and +redundancy; RAID 5 gives you good read speeds but lousy write speeds. + + + + +A journalling filesystem will drastically reduce your reboot time in the +event of a system crash. Currently, +ext3 + will work correctly with NFS +version 3. In addition, Reiserfs version 3.6 will work with NFS version 3 on +2.4.7 or later kernels (patches are available for previous kernels). Earlier versions +of Reiserfs did not include room for generation numbers in the inode, exposing +the possibility of undetected data corruption during a server reboot. + + + + +Additionally, journalled file systems can be configured to maximize +performance by taking advantage of the fact that journal updates are all that +is necessary for data protection. One example is using ext3 with data=journal +so that all updates go first to the journal, and later to the main file +system. Once the journal has been updated, the NFS server can safely issue the +reply to the clients, and the main file system update can occur at the +server's leisure. + + +The journal in a journalling file system may also reside on a separate device +such as a flash memory card so that journal updates normally require no seeking. With only rotational +delay imposing a cost, this gives reasonably good synchronous IO performance. +Note that ext3 currently supports journal relocation, and ReiserFS will +(officially) support it soon. The Reiserfs tool package found at +ftp://ftp.namesys.com/pub/reiserfsprogs/reiserfsprogs-3.x.0k.tar.gz +contains +the reiserfstune tool, which will allow journal relocation. It does, however, +require a kernel patch which has not yet been officially released as of +January, 2002. + + + +Using an automounter (such as autofs or amd) may prevent hangs if you +cross-mount files on your machines (whether on purpose or by oversight) and +one of those machines goes down. See the Automount Mini-HOWTO for details. + + + + +Some manufacturers (Network Appliance, Hewlett Packard, and others) provide NFS +accelerators in the form of Non-Volatile RAM. NVRAM will boost access speed to +stable storage up to the equivalent of async access. + + + - diff --git a/LDP/howto/docbook/NFS-HOWTO/preamble.sgml b/LDP/howto/docbook/NFS-HOWTO/preamble.sgml index f7321053..d4b4e837 100644 --- a/LDP/howto/docbook/NFS-HOWTO/preamble.sgml +++ b/LDP/howto/docbook/NFS-HOWTO/preamble.sgml @@ -3,7 +3,8 @@ Legal stuff -Copyright (c) <2001> by Tavis Barr, Nicolai Langfeldt, and Seth Vidal. +Copyright (c) <2002> by Tavis Barr, Nicolai Langfeldt, +Seth Vidal, and Tom McNeal. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at http://www.opencontent.org/openpub/). @@ -23,7 +24,7 @@ divorce, or any other calamity. Feedback This will never be a finished document; we welcome feedback about - how it can be improved. As of October 2000, the Linux NFS home + how it can be improved. As of February 2002, the Linux NFS home page is being hosted at http://nfs.sourceforge.net. Check there for mailing lists, bug fixes, and updates, and also to verify who currently maintains this document. @@ -57,6 +58,8 @@ The original version of this document was developed by Nicolai Langfeldt. It was heavily rewritten in 2000 by Tavis Barr and Seth Vidal to reflect substantial changes in the workings of NFS for Linux developed between the 2.0 and 2.4 kernels. +It was edited again in February 2002, when Tom McNeal made substantial +additions to the performance section. Thomas Emmel, Neil Brown, Trond Myklebust, Erez Zadok, and Ion Badulescu also provided valuable comments and contributions. diff --git a/LDP/howto/docbook/NFS-HOWTO/security.sgml b/LDP/howto/docbook/NFS-HOWTO/security.sgml index 2ada688b..fad463bb 100644 --- a/LDP/howto/docbook/NFS-HOWTO/security.sgml +++ b/LDP/howto/docbook/NFS-HOWTO/security.sgml @@ -2,48 +2,55 @@ Security and NFS This list of security tips and explanations will not make your site - completely secure. NOTHING will make your site completely secure. This + completely secure. NOTHING will make your site completely secure. Reading this section may help you get an idea of the security problems with NFS. This is not a comprehensive guide and it will always be undergoing changes. If you have any tips or hints to give us please send them to the HOWTO maintainer. - If you're on a network with no access to the outside world (not even a + If you are on a network with no access to the outside world (not even a modem) and you trust all the internal machines and all your users then this section will be of no use to you. However, its our belief that there are relatively few networks in this situation so we would suggest reading this section thoroughly for anyone setting up NFS. - There are two steps to file/mount access in NFS. The first step is mount + With NFS, there are two steps required for a client to gain access to + a file contained in a remote directory on the server. The first step is mount access. Mount access is achieved by the client machine attempting to attach to the server. The security for this is provided by the - /etc/exports file. This file lists the names or ip addresses for machines + /etc/exports file. This file lists the names or IP addresses for machines that are allowed to access a share point. If the client's ip address matches one of the entries in the access list then it will be allowed to mount. This is not terribly secure. If someone is capable of spoofing or taking over a trusted address then they can access your mount points. To give a real-world example of this type of "authentication": This is - equivalent to someone introducing themselves to you and you believe they + equivalent to someone introducing themselves to you and you believing they are who they claim to be because they are wearing a sticker that says - "Hello, My Name is ...." + "Hello, My Name is ...." Once the machine has mounted a volume, its + operating system will have access to all files on the volume (with the + possible exception of those owned by root; see below) and write access + to those files as well, if the volume was exported with the + rw option. The second step is file access. This is a function of normal file system - access controls and not a specialized function of NFS. Once the drive is - mounted the user and group permissions on the files take over access - control. + access controls on the client and not a specialized function of NFS. + Once the drive is mounted the user and group permissions on the files + determine access control. An example: bob on the server maps to the UserID 9999. Bob - makes a file on the server that is only accessible the user (0600 in - octal). A client is allowed to mount the drive where the file is stored. + makes a file on the server that is only accessible the user + (the equivalent to typing + chmod 600 filename). + A client is allowed to mount the drive where the file is stored. On the client mary maps to UserID 9999. This means that the client user mary can access bob's file that is marked as only accessible by him. - It gets worse, if someone has root on the client machine they can - su - [username] and become ANY user. NFS will be none - the wiser. + It gets worse: If someone has become superuser on the client machine they can + su - username + and become any user. NFS will be none the wiser. Its not all terrible. There are a few measures you can take on the server @@ -92,8 +99,8 @@ be careful and keep up diligent monitoring of those systems. - Not all Linux distributions were created equal. Some seemingly up-to- - date distributions do not include a securable portmapper. + Not all Linux distributions were created equal. Some seemingly up-to-date + distributions do not include a securable portmapper. The easy way to check if your portmapper is good or not is to run strings(1) and see if it reads the relevant files, /etc/hosts.deny and /etc/hosts.allow. Assuming your portmapper is /sbin/portmap you can @@ -137,22 +144,28 @@ the mill Linux system there are very few machines that need any access for any reason. The portmapper administers nfsd, mountd, ypbind/ypserv, - pcnfsd, and 'r' services like ruptime and rusers. + rquotad, lockd (which shows up + as nlockmgr), statd + (which shows up as status) + and 'r' services like ruptime + and rusers. Of these only nfsd, mountd, ypbind/ypserv and perhaps - pcnfsd are of any consequence. All machines that need + rquotad,lockd + and statd are of any consequence. All machines that need to access services on your machine should be allowed to do that. Let's say that your machine's address is 192.168.0.254 and that it lives on the subnet 192.168.0.0, and that all - machines on the subnet should have access to it (those are terms introduced - by the Networking-Overview-HOWTO, - go back and refresh your memory if you need to). Then we write: + machines on the subnet should have access to it (for an overview of those + terms see the the Networking-Overview-HOWTO). Then we write: portmap: 192.168.0.0/255.255.255.0 - in /etc/hosts.allow. This is the same as the network - address you give to route and the subnet mask you give to ifconfig. For the - device eth0 on this machine ifconfig should show: + in /etc/hosts.allow. If you are not sure what your + network or netmask are, you can use the ifconfig command to + determine the netmask and the netstat command to + determine the network. For, example, for the + device eth0 on the above machine ifconfig should show: @@ -175,7 +188,7 @@ 192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 174412 eth0 ... - (Network address in first column). + (The network address is in the first column). The /etc/hosts.deny and /etc/hosts.allow files are @@ -194,28 +207,29 @@ hosts.allow and hosts.deny files, so you should put in entries for lockd, statd, mountd, and - rquotad in these files too. + rquotad in these files too. For a complete example, + see . The above things should make your server tighter. The only remaining - problem (Yeah, right!) is someone breaking root (or boot MS-DOS) on a - trusted machine and using that privilege to send requests from a - secure port as any user they want to be. + problem is if someone gains administrative access to one of your trusted + client machines and is able to send bogus NFS requests. The next section + deals with safeguards against this problem. Server security: nfsd and mountd - On the server we can decide that we don't want to trust the client's - root account. We can do that by using the root_squash option in - /etc/exports: + On the server we can decide that we don't want to trust any requests + made as root on the client. We can do that by using the + root_squash option in /etc/exports: /home slave1(rw,root_squash) This is, in fact, the default. It should always be turned on unless you - have a VERY good reason to turn it off. To turn it off use the + have a very good reason to turn it off. To turn it off use the no_root_squash option. @@ -239,10 +253,11 @@ The TCP ports 1-1024 are reserved for root's use (and therefore sometimes referred to as "secure ports") A non-root user cannot bind these ports. - Adding the secure option to an /etc/exports entry forces it to run on a - port below 1024, so that a malicious non-root user cannot come along and - open up a spoofed NFS dialogue on a non-reserved port. This option is set - by default. + Adding the secure option to an + /etc/exports means that it will only listed to + requests coming from ports 1-1024 on the client, so that a malicious + non-root user on the client cannot come along and open up a spoofed + NFS dialogue on a non-reserved port. This option is set by default. @@ -252,19 +267,23 @@ On the client we can decide that we don't want to trust the server too much a couple of ways with options to mount. For example we can - forbid suid programs to work off the NFS file system with the nosuid + forbid suid programs to work off the NFS file system with the + nosuid option. Some unix programs, such as passwd, are called "suid" programs: They set the id of the person running them to whomever is the owner of the file. If a file is owned by root and is suid, then the program will execute as root, so that they can perform operations (such as writing to - the password file) that only root is allowed to do. Using the nosuid + the password file) that only root is allowed to do. Using the + nosuid option is a good idea and you should consider using this with all NFS - mounted disks. It means that the server's root user cannot make a suid-root + mounted disks. It means that the server's root user + cannot make a suid-root program on the file system, log in to the client as a normal user and then use the suid-root program to become root on the client too. One could also forbid execution of files on the mounted file system altogether with the noexec option. - But this is more likely to be impractical than nosuid since a file + But this is more likely to be impractical than + nosuid since a file system is likely to at least contain some scripts or programs that need to be executed. @@ -295,7 +314,7 @@ Securing portmapper, rpc.statd, and rpc.lockd on the client - In the current (2.2.18+) implementation of nfs, full file locking is + In the current (2.2.18+) implementation of NFS, full file locking is supported. This means that rpc.statd and rpc.lockd must be running on the client in order for locks to function correctly. These services require the portmapper to be running. So, most of the @@ -310,20 +329,21 @@ IPchains (under the 2.2.X kernels) and netfilter (under the 2.4.x kernels) allow a good level of security - instead of relying on the - daemon (or in this case the tcp wrapper) to determine who can connect, + daemon (or perhaps its TCP wrapper) to + determine which machines can connect, the connection attempt is allowed or disallowed at a lower level. In - this case you canstop the connection much earlier and more globaly which + this case, you can stop the connection much earlier and more globally, which can protect you from all sorts of attacks. Describing how to set up a Linux firewall is well beyond the scope of - this document. Interested readers may wish to read the Firewall-HOWTO + this document. Interested readers may wish to read the Firewall-HOWTO or the IPCHAINS-HOWTO. For users of kernel 2.4 and above you might want to visit the netfilter webpage at: http://netfilter.filewatcher.org. If you are already familiar with the workings of ipchains or netfilter this section will give you a few tips on how to better setup your - firewall to work with NFS. + NFS daemons to more easily firewall and protect them. A good rule to follow for your firewall configuration is to deny all, and @@ -331,103 +351,290 @@ than you intended. - Ports to be concerned with: - - - The portmapper is on 111. (tcp and udp) - - - - nfsd is on 2049 and it can be TCP and UDP. Although NFS over TCP - is currently experimental on the server end and you will usually - just see UDP on the server, using TCP is quite stable on the - client end. - - - - - mountd, lockd, and statd - float around (which is why we need the portmapper to begin with) - this causes - problems. You basically have two options to deal with it: - - - - You more can more or less do a deny all on connecting ports - but explicitly allow most ports certain ips. - - - - - More recent versions of these utilities have a "-p" option - that allows you to assign them to a certain port. See the - man pages to be sure if your version supports this. You can - then allow access to the ports you have specified for your - NFS client machines, and seal off all other ports, even for - your local network. - - - - - - - - - Using IPCHAINS, a simply firewall using the first option would look - something like this: - - ipchains -A input -f -j ACCEPT - ipchains -A input -s trusted.net.here/trusted.netmask -d host.ip/255.255.255.255 -j ACCEPT - ipchains -A input -s 0/0 -d 0/0 -p 6 -j DENY -y -l - ipchains -A input -s 0/0 -d 0/0 -p 17 -j DENY -l - - - - The equivalent set of commands in netfilter (the firewalling tool in 2.4) is: - - iptables -A INPUT -f -j ACCEPT - iptables -A INPUT -s trusted.net.here/trusted.netmask -d \ - host.ip/255.255.255.255 -j ACCEPT - iptables -A INPUT -s 0/0 -d 0/0 -p 6 -j DENY --syn --log-level 5 - iptables -A INPUT -s 0/0 -d 0/0 -p 17 -j DENY --log-level 5 - - - - The first line says to accept all packet fragments (except the first - packet fragment which will be treated as a normal packet). In theory - no packet will pass through until it is reassembled, and it won't be - reassembled unless the first packet fragment is passed. Of course - there are attacks that can be generated by overloading a machine - with packet fragments. But NFS won't work correctly unless you - let fragments through. See for details. - - - The other three lines say trust your local networks and deny and log - everything else. It's not great and more specific rules pay off, but - more specific rules are outside of the scope of this discussion. - - - Some pointers if you'd like to be more paranoid or strict about your - rules. If you choose to reset your firewall rules each time statd, - rquotad, mountd or lockd - move (which is possible) you'll want to make sure you allow fragments to - your nfs server FROM your nfs client(s). If you don't you will get some very - interesting reports from the kernel regarding packets being denied. The messages - will say that a packet from port 65535 on the client to 65535 on the server - is being denied. Allowing fragments will solve this. - + In order to understand how to firewall the NFS daemons, it will help + to breifly review how they bind to ports. + + +When a daemon starts up, it requests a free port from the portmapper. +The portmapper gets the port for the daemon and keeps track of +the port currently used by that daemon. When other hosts or processes +need to communicate with the daemon, they request the port number +from the portmapper in order to find the +daemon. So the ports will perpetually float because different ports may +be free at different times and so the portmapper will allocate them +differently each time. This is a pain for setting up a firewall. If +you never know where the daemons are going to be then you don't +know precisely which ports to allow access to. This might not be a big deal +for many people running on a protected or isolated LAN. For those +people on a public network, though, this is horrible. + + +In kernels 2.4.13 and later with nfs-utils 0.3.3 or later you no +longer have to worry about the floating of ports in the portmapper. +Now all of the daemons pertaining to nfs can be "pinned" to a port. +Most of them nicely take a -p option when they are started; +those daemons that are started by the kernel take some kernel arguments +or module options. They are described below. + + +Some of the daemons involved in sharing data via nfs are already +bound to a port. portmap is always on port +111 tcp and udp. nfsd is +always on port 2049 TCP and UDP (however, as of kernel 2.4.17, NFS over +TCP is considered experimental and is not for use on production machines). + + +The other daemons, statd, mountd, +lockd, and rquotad, will normally move +around to the first available port they are informed of by the portmapper. + + +To force statd to bind to a particular port, use the +-p +portnum option. To force statd to +respond on a particular port, additionally use the +-o portnum option when starting it. + + +To force mountd to bind to a particular port use the +-p portnum option. + + +For example, to have statd broadcast of port 32765 and listen on port +32766, and mountd listen on port 32767, you would type: + + +# statd -p 32765 -o 32766 +# mountd -p 32767 + + +lockd is started by the kernel when it is needed. +Therefore you need +to pass module options (if you have it built as a module) or kernel +options to force lockd to listen and respond +only on certain ports. + + +If you are using loadable modules and you would like to specify these +options in your /etc/modules.conf file add +a line like this to the file: + + +options lockd nlm.uddpport=32768 nlm.tcpport=32768 + + +The above line would specify the udp and tcp port for +lockd to be 32768. + + +If you are not using loadable modules or if you have compiled +lockd into the kernel instead of building it + as a module then you will need to pass it an option on the kernel boot line. + + +It should look something like this: + + + vmlinuz 3 root=/dev/hda1 lockd.udpport=32768 lockd.tcpport=32768 + + +The port numbers do not have to match but it would simply add +unnecessary confusion if they didn't. + + +If you are using quotas and using rpc.quotad to make these +quotas viewable over nfs you will need to also take it into +account when setting up your firewall. There are two +rpc.rquotad +source trees. One of those is maintained in the +nfs-utils tree. +The other in the quota-tools tree. +They do not operate identically. +The one provided with nfs-utils supports +binding the daemon to a port with the -p +directive. The one in quota-tools does not. +Consult your distribution's documentation to determine if yours does. + + +For the sake of this discussion lets describe a network and setup a +firewall to protect our nfs server. +Our nfs server is 192.168.0.42 our client is 192.168.0.45 only. +As in the example above, statd has been +started so that it only +binds to port 32765 for incoming requests and it must answer on +port 32766. mountd is forced to bind to port 32767. +lockd's module parameters have been set to bind to 32768. +nfsd is, of course, on port 2049 and the portmapper is on port 111. + + +We are not using quotas. + + +Using IPCHAINS, a simple firewall +might look something like this: + + +ipchains -A input -f -j ACCEPT -s 192.168.0.45 +ipchains -A input -s 192.168.0.45 -d 0/0 32765:32768 -p 6 -j ACCEPT +ipchains -A input -s 192.168.0.45 -d 0/0 32765:32768 -p 17 -j ACCEPT +ipchains -A input -s 192.168.0.45 -d 0/0 2049 -p 17 -j ACCEPT +ipchains -A input -s 192.168.0.45 -d 0/0 2049 -p 6 -j ACCEPT +ipchains -A input -s 192.168.0.45 -d 0/0 111 -p 6 -j ACCEPT +ipchains -A input -s 192.168.0.45 -d 0/0 111 -p 17 -j ACCEPT +ipchains -A input -s 0/0 -d 0/0 -p 6 -j DENY -y -l +ipchains -A input -s 0/0 -d 0/0 -p 17 -j DENY -l + + +The equivalent set of commands in netfilter is: + + +iptables -A INPUT -f -j ACCEPT -s 192.168.0.45 +iptables -A INPUT -s 192.168.0.45 -d 0/0 32765:32768 -p 6 -j ACCEPT +iptables -A INPUT -s 192.168.0.45 -d 0/0 32765:32768 -p 17 -j ACCEPT +iptables -A INPUT -s 192.168.0.45 -d 0/0 2049 -p 17 -j ACCEPT +iptables -A INPUT -s 192.168.0.45 -d 0/0 2049 -p 6 -j ACCEPT +iptables -A INPUT -s 192.168.0.45 -d 0/0 111 -p 6 -j ACCEPT +iptables -A INPUT -s 192.168.0.45 -d 0/0 111 -p 17 -j ACCEPT +iptables -A INPUT -s 0/0 -d 0/0 -p 6 -j DENY --syn --log-level 5 +iptables -A INPUT -s 0/0 -d 0/0 -p 17 -j DENY --log-level 5 + + + +The first line says to accept all packet fragments (except the +first packet fragment which will be treated as a normal packet). +In theory no packet will pass through until it is reassembled, +and it won't be reassembled unless the first packet fragment +is passed. Of course there are attacks that can be generated +by overloading a machine with packet fragments. But NFS won't +work correctly unless you let fragments through. See +for details. + + +The other lines allow specific connections from any port on our +client host to the specific ports we have made available on +our server. This means that if, say, 192.158.0.46 attempts to contact +the NFS server it will not be able to mount or see what mounts +are available. + + +With the new port pinning capabilities it is obviously much easier +to control what hosts are allowed to mount your NFS shares. It is +worth mentioning that NFS is not an encrypted protocol and anyone +on the same physical network could sniff the traffic and reassemble +the information being passed back and forth. + + + Tunneling NFS through SSH + +One method of encrypting NFS traffic over a network is to +use the port-forwarding capabilities of ssh. +However, as we shall see, doing so has a serious drawback if you do not +utterly and completely trust the local users on your server. + + +The first step will be to export files to the localhost. For example, to +export the /home partition, enter the following into +/etc/exports: + +/home 127.0.0.1(rw) + + + +The next step is to use ssh to forward ports. For example, +ssh can tell the server to forward to any port on any +machine from a port on the client. Let us assume, as in the previous +section, that our server is 192.168.0.42, and that we have pinned +mountd to port 32767 +using the argument -p 32767. Then, on the client, +we'll type: + + # ssh root@192.168.0.42 -L 250:localhost:2049 -f sleep 60m + # ssh root@192.168.0.42 -L 251:localhost:32767 -f sleep 60m + + + +The above command causes ssh on the client to take +any request directed at the client's port 250 and forward it, +first through sshd on the server, and then on + to the server's port 2049. The second line +causes a similar type of forwarding between requests to port 251 on +the client and port 32767 on the server. The +localhost is relative to the server; that is, +the forwarding will be done to the server itself. The port could otherwise +have been made to forward to any other machine, and the requests would look to +the outside world as if they were coming from the server. Thus, the requests +will appear to NFSD on the server as if they are coming from the server itself. +Note that in order to bind to a port below 1024 on the client, we have +to run this command as root on the client. Doing this will be necessary +if we have exported our filesystem with the default +secure option. + + +Finally, we are pulling a little trick with the last option, +-f sleep 60m. Normally, when +we use ssh, even with the -L option, +we will open up a shell on the remote machine. But instead, we just want +the port forwarding to execute in the background so that we get our shell +on the client back. So, we tell ssh to execute a command +in the background on the server to sleep for 60 minutes. This will cause +the port to be forwarded for 60 minutes until it gets a connection; at that +point, the port will continue to be forwarded until the connection dies or +until the 60 minutes are up, whichever happens later. The above command +could be put in our startup scripts on the client, right after the network +is started. + + + Next, we have to mount the filesystem on the client. To do this, we tell + the client to mount a filesystem on the localhost, but at a different + port from the usual 2049. Specifically, an entry in /etc/fstab + would look like: + + localhost:/home /mnt/home nfs rw,hard,intr,port=250,mountport=251 0 0 + + +Having done this, we can see why the above will be incredibly insecure +if we have any ordinary users who are able to log in +to the server locally. If they can, there is nothing preventing them from +doing what we did and using ssh to forward a privileged +port on their own client machine (where they are legitimately root) to ports +2049 and 32767 on the server. Thus, any ordinary user on the server can +mount our filesystems with the same rights as root on our client. + + +If you are using an NFS server that does not have a way for ordinary users +to log in, and you wish to use this method, there are two additional caveats: +First, the connection travels from the client to the server via +sshd; therefore you will have to leave port 22 (where +sshd listens) open to your client on the firewall. However +you do not need to leave the other ports, such as 2049 and 32767, open +anymore. Second, file locking will no longer work. It is not possible +to ask statd or the locking manager to make requests +to a particular port for a particular mount; therefore, any locking requests +will cause statd to connect to statd +on localhost, i.e., itself, and it will fail with an error. Any attempt +to correct this would require a major rewrite of NFS. + + +It may also be possible to use IPSec to encrypt +network traffic between your client and your server, without compromising +any local security on the server; this will not be taken up here. +See the FreeS/WAN home page +for details on using IPSec under Linux. + + Summary If you use the hosts.allow, hosts.deny, - root_squash, nosuid and privileged - port features in the portmapper/nfs software you avoid many of the - presently known bugs in nfs and can almost feel secure about that at + root_squash, nosuid and privileged + port features in the portmapper/NFS software, you avoid many of the + presently known bugs in NFS and can almost feel secure about that at least. But still, after all that: When an intruder has access to your network, s/he can make strange commands appear in your .forward or read your mail when /home or /var/mail is NFS exported. For the same reason, you should never access your PGP private key - over nfs. Or at least you should know the risk involved. And now you know a bit + over NFS. Or at least you should know the risk involved. And now you know a bit of it. @@ -438,4 +645,3 @@ - diff --git a/LDP/howto/docbook/NFS-HOWTO/server.sgml b/LDP/howto/docbook/NFS-HOWTO/server.sgml index c008c7be..5cef412b 100644 --- a/LDP/howto/docbook/NFS-HOWTO/server.sgml +++ b/LDP/howto/docbook/NFS-HOWTO/server.sgml @@ -59,9 +59,11 @@ client machines that will have access to the directory. The machines - may be listed by their IP address or their DNS address + may be listed by their DNS address or their IP address (e.g., machine.company.com or 192.168.0.8). - Using IP addresses is more reliable and more secure. + Using IP addresses is more reliable and more secure. If you need to + use DNS addresses, and they do not seem to be resolving to the right + machine, see . @@ -85,11 +87,14 @@ - no_root_squash: By default, any file request made by user root + no_root_squash: By default, + any file request made by user root on the client machine is treated as if it is made by user - nobody on the server. (Excatly which UID the request is + nobody on the + server. (Excatly which UID the request is mapped to depends on the UID of user "nobody" on the server, - not the client.) If no_root_squash is selected, then + not the client.) If no_root_squash + is selected, then root on the client machine will have the same level of access to the files on the system as root on the server. This can have serious security implications, although it may be @@ -109,19 +114,17 @@ - sync: By default, a Version 2 NFS server will tell a client - machine that a file write is complete when NFS has finished - handing the write over to the filesysytem; however, the file - system may not sync it to the disk, even if the client makes - a sync() call on the file system. The default behavior may - therefore cause file corruption if the server reboots. This - option forces the filesystem to sync to disk every time NFS - completes a write operation. It slows down write times - substantially but may be necessary if you are running NFS - Version 2 in a production environment. Version 3 NFS has - a commit operation that the client can call that - actually will result in a disk sync on the server end. - + sync: + By default, all but the most recent version (version 1.11) + of the exportfs command will use + async behavior, telling a client + machine that a file write is complete - that is, has been written + to stable storage - when NFS has finished handing the write over to + the filesysytem. This behavior may cause data corruption if the + server reboots, and the sync option prevents + this. See for a complete discussion of + sync and async behavior. + @@ -174,7 +177,9 @@ Third, you can use wildcards such as *.foo.com or - 192.168. instead of hostnames. + 192.168. instead of hostnames. There were problems + with wildcard implementation in the 2.2 kernel series that were fixed + in kernel 2.2.19. However, you should keep in mind that any of these simplifications @@ -205,7 +210,8 @@ /etc/hosts.allow and /etc/hosts.deny These two files specify which computers on the network can use - services on your machine. Each line of the file is an entry listing + services on your machine. Each line of the file + contains a single entry listing a service and a set of machines. When the server gets a request from a machine, it does the following: @@ -232,7 +238,8 @@ - In addition to controlling access to services handled by inetd (such + In addition to controlling access to services + handled by inetd (such as telnet and FTP), this file can also control access to NFS by restricting connections to the daemons that provide NFS services. Restrictions are done on a per-service basis. @@ -257,8 +264,8 @@ In general it is a good idea with NFS (as with most internet services) - to explicitly deny access to hosts that you don't need to allow access - to. + to explicitly deny access to IP addresses that you don't need + to allow access to. The first step in doing this is to add the followng entry to @@ -270,10 +277,10 @@ - Starting with nfs-utils 0.2.0, you can be a bit more careful by + Starting with nfs-utils 0.2.0, you can be a bit more careful by controlling access to individual daemons. It's a good precaution since an intruder will often be able to weasel around the portmapper. - If you have a newer version of NFS-utils, add entries for each of the + If you have a newer version of nfs-utils, add entries for each of the NFS daemons (see the next section to find out what these daemons are; for now just put entries for them in hosts.deny): @@ -286,7 +293,7 @@ - Even if you have an older version of nfs-utils, adding these entries + Even if you have an older version of nfs-utils, adding these entries is at worst harmless (since they will just be ignored) and at best will save you some trouble when you upgrade. Some sys admins choose to put the entry ALL:ALL in the file /etc/hosts.deny, @@ -310,7 +317,7 @@ Here, host is IP address of a potential client; it may be possible in some versions to use the DNS name of the host, but it is strongly - deprecated. + discouraged. Suppose we have the setup above and we just want to allow access @@ -351,7 +358,8 @@ The NFS server should now be configured and we can start it running. First, you will need to have the appropriate packages installed. This consists mainly of a new enough kernel and a new enough version - of the nfs-utils package. See if you are in doubt. + of the nfs-utils package. + See if you are in doubt. Next, before you can start NFS, you will need to have TCP/IP @@ -366,7 +374,8 @@ Verifying that NFS is running. If this does not work, or if you are not in a position to reboot your machine, then the following section will tell you which daemons need to be started in order to - run NFS services. If for some reason nfsd was already running when + run NFS services. If for some reason nfsd + was already running when you edited your configuration files above, you will have to flush your configuration; see for details. @@ -385,13 +394,15 @@ The Daemons - NFS serving is taken care of by five daemons: rpc.nfsd, which does - most of the work; rpc.lockd and rpc.statd, which handle file locking; - rpc.mountd, which handles the initial mount requests, and - rpc.rquotad, which handles user file quotas on exported volumes. - Starting with 2.2.18, lockd is called by nfsd upon demand, so you do - not need to worry about starting it yourself. statd will need to be - started separately. Most recent Linux distributions will + NFS serving is taken care of by five daemons: rpc.nfsd, + which does most of the work; rpc.lockd and + rpc.statd, which handle file locking; + rpc.mountd, which handles the initial mount requests, + and rpc.rquotad, which handles user file quotas on + exported volumes. Starting with 2.2.18, lockd + is called by nfsd upon demand, so you do + not need to worry about starting it yourself. statd + will need to be started separately. Most recent Linux distributions will have startup scripts for these daemons. @@ -403,9 +414,9 @@ then then you should add them, configured to start in the following order: - rpc.portmap - rpc.mountd, rpc.nfsd - rpc.statd, rpc.lockd (if necessary), rpc.rquotad + rpc.portmap + rpc.mountd, rpc.nfsd + rpc.statd, rpc.lockd (if necessary), and rpc.rquotad @@ -461,9 +472,12 @@ such as Solaris default to TCP. - If you do not at least see a line that says "portmapper", a line - that says "nfs", and a line that says "mountd" then you will need - to backtrack and try again to start up the daemons (see , + If you do not at least see a line that says + portmapper, a line that says + nfs, and a line that says + mountd then you will need + to backtrack and try again to start up the daemons + (see , Troubleshooting, if this still doesn't work). @@ -476,16 +490,16 @@ If you come back and change your /etc/exports file, the changes you make may not take effect immediately. You should run the command - exportfs -ra to force nfsd to re-read the /etc/exports -  file. If you can't find the exportfs command, then you can kill nfsd with the + exportfs -ra to force nfsd to re-read the /etc/exports +  file. If you can't find the exportfs command, then you can kill nfsd with the -HUP flag (see the man pages for kill for details). If that still doesn't work, don't forget to check hosts.allow to make sure you haven't forgotten to list any new client machines there. Also check the host listings on any firewalls you may have - set up (see for more details on firewalls - and NFS). + set up (see and + for more details on firewalls and NFS). diff --git a/LDP/howto/docbook/NFS-HOWTO/troubleshooting.sgml b/LDP/howto/docbook/NFS-HOWTO/troubleshooting.sgml index b49a5cad..62d5fa15 100644 --- a/LDP/howto/docbook/NFS-HOWTO/troubleshooting.sgml +++ b/LDP/howto/docbook/NFS-HOWTO/troubleshooting.sgml @@ -15,9 +15,10 @@ There are several ways of doing this. The most reliable way is to look at the file /proc/mounts, which will list all mounted filesystems and give details about them. If - this doesn't work (for example if you don't have the /proc + this doesn't work (for example if you don't + have the /proc filesystem compiled into your kernel), you can type - 'mount -f' although you get less information. + mount -f although you get less information. If the file system appears to be mounted, then you may @@ -50,7 +51,8 @@ - failed, reason given by server: Permission denied + failed, reason given by server: + Permission denied This means that the server does not recognize that you @@ -63,7 +65,8 @@ volume is exported and that your client has the right kind of access to it. For example, if a client only has read access then you have to mount the volume - with the ro option rather than the rw option. + with the ro option rather + than the rw option. @@ -88,16 +91,33 @@ in /etc/hosts that is throwing off the server, or you may not have listed the client's complete address and it may be resolving to a machine in a different - domain. Try to ping the client from the server, and try - to ping the server from the client. If this doesn't work, + domain. One trick is login to the server from the + client via ssh or telnet; + if you then type who, one of the listings + should be your login session and the name of your client + machine as the server sees it. Try using this machine name + in your /etc/exports entry. + Finally, try to ping the client from the server, and try + to ping the server from the client. If this doesn't work, or if there is packet loss, you may have lower-level network problems. + + + It is not possible to export both a directory and its child + (for example both + /usr and /usr/local). + You should export the parent directory with the necessary + permissions, and all of its subdirectories can then be + mounted with those same permissions. + + - RPC: Program Not Registered (or another "RPC" error): + + RPC: Program Not Registered: (or another "RPC" error): This means that the client does not detect NFS running on the server. This could be for several reasons. @@ -136,13 +156,15 @@ This says that we have NFS versions 2 and 3, rpc.statd version 1, network lock manager (the service name for - rpc.lockd) versions 1, 3, and 4. There are also different + rpc.lockd) versions 1, 3, and 4. + There are also different service listings depending on whether NFS is travelling over TCP or UDP. UDP is usually (but not always) the default unless TCP is explicitly requested. - If you do not see at least portmapper, nfs, and mountd, then + If you do not see at least portmapper, nfs, and + mountd, then you need to restart NFS. If you are not able to restart successfully, proceed to . @@ -150,8 +172,9 @@ Now check to make sure you can see it from the client. - On the client, type rpcinfo -p [server] where - [server] is the DNS name or IP address of your server. + On the client, type rpcinfo -p + server where server + is the DNS name or IP address of your server. If you get a listing, then make sure that the type @@ -160,13 +183,14 @@ NFS, make sure Version 3 is listed; if you are trying to mount using NFS over TCP, make sure that is registered. (Some non-Linux clients default to TCP). - See man rpcinfo for more details on how + Type man rpcinfo for more details on how to read the output. If the type of mount you are trying to perform is not listed, try a different type of mount. - If you get the error No Remote Programs Registered, + If you get the error + No Remote Programs Registered, then you need to check your /etc/hosts.allow and /etc/hosts.deny files on the server and make sure your client actually is allowed access. Again, if the @@ -176,9 +200,11 @@ the client. Also check the error logs on the system for helpful messages: Authentication errors from bad /etc/hosts.allow entries will usually appear in - /var/log/messages, but may appear somewhere else depending + /var/log/messages, + but may appear somewhere else depending on how your system logs are set up. The man pages - for syslog can help you figure out how your logs are + for syslog can + help you figure out how your logs are set up. Finally, some older operating systems may behave badly when routes between the two machines are asymmetric. Try typing tracepath [server] from @@ -188,8 +214,9 @@ not usually a problem on recent linux distributions. - If you get the error Remote system error - No route - to host, but you can ping the server correctly, + If you get the error + Remote system error - No route to host, + but you can ping the server correctly, then you are the victim of an overzealous firewall. Check any firewalls that may be set up, either on the server or on any routers in between @@ -221,7 +248,7 @@ /proc/mounts and make sure the volume is mounted read/write (although if it is mounted read-only you ought to get a more specific error message). If not then - you need to re-mount with the rw option. + you need to re-mount with the rw option. The second problem has to do with username mappings, and is @@ -292,7 +319,8 @@ - These happen when a NFS setattr operation is attempted on a + These happen when a NFS setattr + operation is attempted on a file you don't have write access to. The messages are harmless. @@ -309,8 +337,8 @@ - The "can't get a request slot" message means that the client- - side RPC code has detected a lot of timeouts (perhaps due to + The "can't get a request slot" message means that the client-side + RPC code has detected a lot of timeouts (perhaps due to network congestion, perhaps due to an overloaded server), and is throttling back the number of concurrent outstanding requests in an attempt to lighten the load. The cause of @@ -336,7 +364,7 @@ nfs warning: mount version older than kernel - Errors in startup/shutdown log for lockd + Errors in startup/shutdown log for lockd You may see a message of the following kind in your boot log: @@ -345,10 +373,12 @@ nfslock: rpc.lockd startup failed - They are harmless. Older versions of rpc.lockd needed to be + They are harmless. Older versions of rpc.lockd needed to be started up manually, but newer versions are started automatically - by knfsd. Many of the default startup scripts still try to start - up lockd by hand, in case it is necessary. You can alter your + by nfsd. Many of the + default startup scripts still try to start + up lockd by hand, in case + it is necessary. You can alter your startup scripts if you want the messages to go away. @@ -376,19 +406,19 @@ kmem_create: forcing size word alignment - nfs_fh Symptom 7 - - /etc/exports is VERY sensitive to whitespace - so the + /etc/exports is very sensitive to whitespace - so the following statements are not the same: - /export/dir hostname(rw,no_root_squash) /export/dir hostname (rw,no_root_squash) - The first will grant hostname rw access to /export/dir + The first will grant hostname rw + access to /export/dir without squashing root privileges. The second will grant - hostname rw privs w/root squash and it will grant EVERYONE - else read-write access, without squashing root privileges. - Nice huh? + hostname rw privileges with + root squash and it will grant + everyone else read/write access, without + squashing root privileges. Nice huh? @@ -412,8 +442,10 @@ kmem_create: forcing size word alignment - nfs_fh - You may be using a larger rsize and wsize in your mount options - than the server supports. Try reducing rsize and wsize to 1024 and + You may be using a larger rsize + and wsize in your mount options + than the server supports. Try reducing rsize + and wsize to 1024 and seeing if the problem goes away. If it does, then increase them slowly to a more reasonable value. @@ -430,6 +462,19 @@ kmem_create: forcing size word alignment - nfs_fh to reinstall your binaries if none of these ideas helps. + + File Corruption When Using Multiple Clients + Symptom 10 + + If a file has been modified within one second of its + previous modification and left the same size, it will + continue to generate the same inode number. Because + of this, constant reads and writes to a file by + multiple clients may cause file corruption. Fixing + this bug requires changes deep within the filesystem + layer, and therefore it is a 2.5 item. + +