diff --git a/LDP/howto/docbook/Small-Memory.sgml b/LDP/howto/docbook/Small-Memory.sgml new file mode 100644 index 00000000..6d0be587 --- /dev/null +++ b/LDP/howto/docbook/Small-Memory.sgml @@ -0,0 +1,162 @@ + +
+ + Small Memory mini-HOWTO + + Todd + Burgess + +
tburgess@uoguelph.ca
+ + + + Describes how to run Linux on a system with a small amount of + memory. + + 2000-12-12 + + + 0.1 + 2000-12-01 + tb + + + + + Introduction + Assuming buying more memory is out of the question there are many + things you can do to tighten up memory usage in Linux. + Many Linux distributions out of the box are quite bloated from a + memory perspective. They run more services and offer more features than most of + us will ever need. By removing many of these services you can free up several + megabytes of real memory. + My own system is a 486DX2-66 with 12MB of physical memory and 12MB + of swap space. It has run Linux for the last 3 years quite happily, and + hopefully it will run Linux for several more years. :) + + + Linux Kernel + All the Linux kernels which come with distributions are quite + bloated and contain more features than any of us will ever need or use. If you + have not re-compiled your own kernel, it is highly recommended that you do so. + How to re-compile a kernel is beyond the scope of this document, but many + excellent Linux books and guides cover this subject in intimate detail. + If you do re-compile your kernel, remember to put in no more + features than you need. For instance: how many of you include PLIP support in + your kernel? How many of you who include it actually use it? Smaller kernels + require less time to load, use less memory, and use less CPU cycles. + Another thing is modules. I personally do not use them because I + found them to be a cumbersome. If you use them and like them then they can help + to relieve "kernel bloat." + + + Virtual Consoles + VCs are a great way to free up memory. Most Linux distributions run + about 6 of them out of the box. On average running 6 VCs requires about 4MB of + memory. Removing a couple of them can free up a couple MBs of memory. Most + users can get away with running only 3 or 4 VCs. How many you choose to remove + is a matter personal preference. Just remember that the fewer you run, the more + memory your applications will have to run. + The file which outlines how many VCs get loaded is + /etc/inittab. In order to remove VCs: + + + Load /etc/inittab in a text + editor. + + + Look for a line which looks like the following line (the key + feature being a line which starts with c1): + c1:12345:respawn:/sbin/getty tty1 38400 + linux + Start at the highest number (i.e. c6) and comment it out by + inserting a '#' in the first row. Repeat this step as many times as needed. + Remember every line you comment out is one less VC running. + + + Re-boot the system for your changes to take effect. + + + + + Daemons + Many Linux distributions run daemons most of us will never use. + Most of these daemons are loaded by scripts. Where these scripts are and what + they are called depends on your Linux distribution. Slackware set-up scripts + are buried in /etc/rc.d/rc.*. + Before you proceed, a knowledge of Unix shell script programming + would be a definite asset. However, if you have no experience writing Unix + shell scripts, what follows is probably the quickest introduction to shell + script programming ever written. + Take the following shell script: + #!/bin/sh echo "hello world" + #echo "good bye cruel world" + The previous code will echo the string "hello world". Shell scripts + must contain the the line + "#!/bin/sh" at the very top line. + After that every line is executed as if you had typed it at the keyboard (think + of shell scripts as nothing more then glorified keyboard macros). + Lines which begin with a '#' are said to be commented out because + they do not get executed by the shell. Most start-up scripts when they load + daemons look like: + if somecondition + do something + fi + What you want to do is comment out every line starting with the if + statement and ending with the fi statement. + If you want to find where a daemon is loaded, + search the start-up scripts for the name of the daemon. If I wanted to find + where inetd is loaded in Slackware I would do the following: + $ cd /edt/rc/d $grep -n inetd rd.* + + <application>inetd</application> + inetd allows people to do things like telnet, ftp, and send talk + requests to your machine. If you never use your system as a server or need to + access any of its services remotely you can remove inetd. + + + <application>lpd</application> + lpd is used to print files on your printer using the + lpr command. If you never print on your Linux + box you can remove lpd. If, however, you own a HP Deskjet ™ printer and + would like to print, I highly recommend the package I put together called + dj-printcap which is available at: + + ftp://sunsite.unc.edu/pub/Linux/system/Printing/dj-printcap.tar.gz + + + + <application>nfsd</application> and <application>mountd</application> + These two daemons are used to run an NFS server. If you never use + your Linux system as an NFS server you can safely remove these two daemons. + + + + <application>portmap</application> + The portmap daemon is used to handle RPC services. If you do not + run an NFS server or any other RPC programs you can remove portmap. + + + <application>sendmail</application> + sendmail is another daemon which requires a fair bit of memory. + If you never use your Linux box as a relay for sending e-mail or you never + receive mail on your Linux box, you can probably remove sendmail. If you do send + e-mail from your Linux box most e-mail clients can be set-up to send e-mail + from another mail server. + + + others + There may be other daemons your system starts up which you do + not need. Remove what you feel you have to. Two daemons which you must run are + syslogd and klogd. + + + + Conclusions + The previous discussion illustrates the steps I took to tighten up + my memory usage on my Linux box. Hopefully I have provided you with some + insight into what you can do with your Linux box to conserve memory. Good luck + and happy hacking! + +