mirror of https://github.com/mkerrisk/man-pages
Varous rewordings; clear up some imprecisions.
This commit is contained in:
Michael Kerrisk
parent
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commit
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202
man2/syscalls.2
202
man2/syscalls.2
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@ -34,8 +34,33 @@ Linux system calls.
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.SH DESCRIPTION
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The system call is the fundamental interface between an application
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and the Linux kernel.
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.SS System calls and library wrapper functions
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System calls are generally not invoked directly,
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but rather via wrapper functions in glibc (or perhaps some other libc).
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Often, but not always, the name of the wrapper function is the same
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as the name of the system call that it invokes.
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For example, glibc contains a function
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.BR truncate ()
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which invokes the underlying "truncate" system call.
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This man page lists those system calls that are common to most platforms.
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Often the glibc wrapper function is quite thin, doing little work
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before invoking the system call.
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Sometimes, however, the wrapper function does some extra work
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before invoking the system call.
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For example, nowadays there are (for reasons described below) two
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related system calls,
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.BR truncate (2)
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and
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.BR truncate64 (2),
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and the glibc
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.BR truncate ()
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wrapper function determines which system call should be employed.
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(This "impedance layer" for programs linked against glibc
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allows new programs to use the more modern version of the underlying
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system calls while preserving the semantics of old binaries.)
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.SS System call list
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Below is a list of those system calls that are common to most platforms.
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In the list, the
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.I Kernel
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column indicates the kernel version
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@ -45,6 +70,8 @@ Note the following points:
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.IP * 3
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Where no kernel version is indicated,
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the system call appeared in kernel 2.0 or earlier.
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.\" kernel 1.2 was started from a branch of 1.0.6
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.\" kernel 2.0 was started from a branch of 1.2.?? (to determine)
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.IP *
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Where a system call is marked "2.2"
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this means the system call probably appeared in a 2.1.x kernel version,
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@ -84,6 +111,8 @@ The list of system calls that are available as at kernel 2.6.22
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.\" instructive about i386 specifics.
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.\"
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.TS
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l l l
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---
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l l l.
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\fBSystem call Kernel Notes\fP
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@ -102,8 +131,7 @@ l l l.
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\fBbind\fP(2)
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\fBbreak\fP(2)
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\fBbrk\fP(2)
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\fBcacheflush\fP(2) Various architectures;
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but not on i386
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\fBcacheflush\fP(2) Not on i386
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\fBcapget\fP(2) 2.2
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\fBcapset\fP(2) 2.2
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\fBchdir\fP(2)
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@ -132,8 +160,9 @@ l l l.
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\fBexit\fP(2)
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\fBexit_group\fP(2) 2.6; 2.4.20
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\fBfaccessat\fP(2) 2.6.16
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\fBfadvise64\fP(2) 2.6 Implements \fBposix_fadvise\fP(2)
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\fBfadvise64_64\fP(2) 2.6 Implements \fBposix_fadvise\fP(2)
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\fBfadvise64\fP(2) 2.6
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.\" Implements \fBposix_fadvise\fP(2)
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\fBfadvise64_64\fP(2) 2.6
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\fBfchdir\fP(2)
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\fBfchmod\fP(2)
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\fBfchmodat\fP(2) 2.6.16
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@ -156,8 +185,8 @@ l l l.
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\fBfstatfs\fP(2)
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\fBfstatfs64\fP(2) 2.6
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\fBfsync\fP(2)
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\fBftime\fP(2) Implemented in glibc;
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see \fBftime\fP(3)
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\fBftime\fP(2)
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.\" Implemented in glibc; see \fBftime\fP(3)
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\fBftruncate\fP(2)
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\fBftruncate64\fP(2) 2.4
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\fBfutex\fP(2) 2.6; 2.4.19
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@ -180,12 +209,12 @@ l l l.
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\fBgetgroups32\fP(2) 2.4
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\fBgetitimer\fP(2)
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\fBgetpeername\fP(2)
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\fBgetpagesize\fP(2) Various architectures;
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but not on i386
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\fBgetpagesize\fP(2) Not on i386
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\fBgetpgid\fP(2)
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\fBgetpgrp\fP(2)
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\fBgetpid\fP(2)
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\fBgetpmsg\fP(2) 2.2 Reserved for STREAMS support
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\fBgetpmsg\fP(2) 2.2
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.\" Reserved for STREAMS support
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\fBgetppid\fP(2)
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\fBgetpriority\fP(2)
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\fBgetresgid\fP(2) 2.2
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@ -219,9 +248,10 @@ l l l.
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\fBiopl\fP(2)
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\fBioprio_get\fP(2) 2.6.13
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\fBioprio_set\fP(2) 2.6.13
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\fBipc\fP(2) Implements System V IPC calls
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\fBkexec_load\fP(2) 2.6.7 Was named sys_kexec_load()
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from 2.6.7 to 2.6.16
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\fBipc\fP(2)
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.\" Implements System V IPC calls
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\fBkexec_load\fP(2) 2.6.7
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.\" Was named sys_kexec_load() from 2.6.7 to 2.6.16
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\fBkeyctl\fP(2) 2.6.11
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\fBkill\fP(2)
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\fBlchown\fP(2) 2.2
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@ -258,8 +288,8 @@ l l l.
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\fBmove_pages\fP(2) 2.6.18
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\fBmprotect\fP(2)
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\fBmpx\fP(2)
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\fBmq_getsetattr\fP(2) 2.6.6 Implements \fBmq_getattr\fP(3)
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and \fBmq_setattr\fP(3)
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\fBmq_getsetattr\fP(2) 2.6.6
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.\" Implements \fBmq_getattr\fP(3) and \fBmq_setattr\fP(3)
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\fBmq_notify\fP(2) 2.6.6
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\fBmq_open\fP(2) 2.6.6
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\fBmq_timedreceive\fP(2) 2.6.6
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@ -287,14 +317,17 @@ l l l.
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\fBopen\fP(2)
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\fBopenat\fP(2) 2.6.16
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\fBpause\fP(2)
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\fBpciconfig_iobase\fP(2) 2.2.15; 2.4 Alpha, PowerPC, ARM; not i386
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\fBpciconfig_read\fP(2) 2.0.26; 2.2 Alpha, PowerPC, ARM; not i386
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\fBpciconfig_write\fP(2) 2.0.26; 2.2 Alpha, PowerPC, ARM; not i386
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\fBpciconfig_iobase\fP(2) 2.2.15; 2.4 Not on i386
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.\" Alpha, PowerPC, ARM; not i386
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\fBpciconfig_read\fP(2) 2.0.26; 2.2 Not on i386
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.\" , PowerPC, ARM; not i386
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\fBpciconfig_write\fP(2) 2.0.26; 2.2 Not on i386
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.\" , PowerPC, ARM; not i386
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\fBpersonality\fP(2)
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.\" \fBperfctr\fP(2) ??? Sparc32, Sparc64
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.\" \fBperfmonctl\fP(2) ??? IA-64
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\fBphys\fP(2) Unimplemented (no slot
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since 2.1.116)
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\fBphys\fP(2)
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.\" Unimplemented (no slot since 2.1.116)
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\fBpipe\fP(2)
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\fBpivot_root\fP(2) 2.5
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\fBpoll\fP(2) 2.2
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@ -303,18 +336,21 @@ l l l.
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\fBpread64\fP(2) Added as "pread" in 2.2;
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renamed "pread64" in 2.6
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\fBprof\fP(2)
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\fBprofil\fP(2) Implemented in glibc;
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see \fBprofil\fP(3)
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\fBpselect6\fP(2) 2.6.16 Implements \fBpselect\fP(2)
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\fBprofil\fP(2)
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.\" Implemented in glibc; see \fBprofil\fP(3)
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\fBpselect6\fP(2) 2.6.16
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.\" Implements \fBpselect\fP(2)
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\fBptrace\fP(2)
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\fBputpmsg\fP(2) 2.2 Reserved for STREAMS support
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\fBputpmsg\fP(2) 2.2
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.\" Reserved for STREAMS support
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\fBpwrite64\fP(2) Added as "pwrite" in 2.2;
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renamed "pwrite64" in 2.6
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\fBquery_module\fP(2) 2.2
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\fBquotactl\fP(2)
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\fBread\fP(2)
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\fBreadahead\fP(2) 2.4.13
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\fBreaddir\fP(2) Superseded by \fBgetdents\fP(2)
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\fBreaddir\fP(2)
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.\" Supersedes \fBgetdents\fP(2)
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\fBreadlink\fP(2)
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\fBreadlinkat\fP(2) 2.6.16
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\fBreadv\fP(2)
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@ -332,7 +368,8 @@ l l l.
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\fBrt_sigaction\fP(2) 2.2
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\fBrt_sigpending\fP(2) 2.2
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\fBrt_sigprocmask\fP(2) 2.2
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\fBrt_sigqueueinfo\fP(2) 2.2 Implements \fBsigqueue\fP(2)
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\fBrt_sigqueueinfo\fP(2) 2.2
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.\" Implements \fBsigqueue\fP(2)
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\fBrt_sigreturn\fP(2) 2.2
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\fBrt_sigsuspend\fP(2) 2.2
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\fBrt_sigtimedwait\fP(2) 2.2
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@ -408,7 +445,8 @@ l l l.
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\fBsigreturn\fP(2)
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\fBsigsuspend\fP(2)
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\fBsocket\fP(2)
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\fBsocketcall\fP(2) Implements BSD socket calls
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\fBsocketcall\fP(2)
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.\" Implements BSD socket calls
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\fBsocketpair\fP(2)
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\fBsplice\fP(2) 2.6.17
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\fBspu_create\fP(2) 2.6.16 PowerPC only
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@ -429,7 +467,8 @@ l l l.
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.\" \fBsys_debug_setcontext\fP(2) ??? PowerPC if CONFIG_PPC32
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\fBsysfs\fP(2)
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\fBsysinfo\fP(2)
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\fBsyslog\fP(2) glibc interface is \fBklogctl\fP(3)
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\fBsyslog\fP(2)
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.\" glibc interface is \fBklogctl\fP(3)
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\fBtee\fP(2) 2.6.17
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\fBtgkill\fP(2) 2.6
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\fBtime\fP(2)
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@ -443,11 +482,12 @@ l l l.
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\fBtkill\fP(2) 2.6; 2.4.22
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\fBtruncate\fP(2)
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\fBtruncate64\fP(2) 2.4
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\fBtuxcall\fP(2) Unimplemented; no slot on i386
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\fBtuxcall\fP(2)
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.\" Unimplemented; no slot on i386
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.\" As at 2.6.22, tuxcall has a slot on PowerPC, x86_64, and alpha
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\fBugetrlimit\fP(2) 2.4
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\fBulimit\fP(2) Implemented in glibc;
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see \fBulimit\fP(3)
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\fBulimit\fP(2)
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.\" Implemented in glibc; see \fBulimit\fP(3)
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\fBumask\fP(2)
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\fBumount\fP(2)
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.\" sys_oldumount() -- __NR_umount
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@ -464,7 +504,8 @@ l l l.
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\fButimes\fP(2) 2.6
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\fBvfork\fP(2)
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\fBvhangup\fP(2)
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\fBvm86old\fP(2) Superseded by \fBvm86\fP(2)
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\fBvm86old\fP(2)
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.\" Superseded by \fBvm86\fP(2)
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\fBvmsplice\fP(2) 2.6.17
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\fBvserver\fP(2) 2.6
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\fBwait4\fP(2)
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@ -474,6 +515,12 @@ l l l.
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\fBwritev\fP(2)
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.TE
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.PP
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On many platforms, including i386, socket calls are all multiplexed
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(via glibc wrapper functions) through
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.BR socketcall (2)
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and similarly System V IPC calls are multiplexed through
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.BR ipc (2).
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.SH NOTES
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Note the following points:
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.IP * 3
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Although slots are reserved for them in the system call table,
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@ -541,17 +588,22 @@ Over time, changes to the interfaces of some system calls have been
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necessary.
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One reason for such changes was the need to increase the size of
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structures or scalar values passed to the system call.
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Because of these changes, there are now multiple implementations
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of certain system calls.
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These different versions are incompatible at the binary level,
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but applications are generally unaware of this: glibc does some magic
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to ensure that existing binaries use the version of the system
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call that was current when the binary was created,
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so that ABI compatibility is preserved.
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Because of these changes, there are now various groups
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of related system calls
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(e.g.,
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.BR truncate (2)
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and
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.BR ftruncate64 (2))
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which perform similar tasks, but which vary in
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details such as the size of their arguments.
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(As noted earlier, applications are generally unaware of this:
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the glibc wrapper functions do some work to ensure that the right
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system call is invoked, and that ABI compatibility is
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preserved for old binaries.)
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Examples of systems calls that exist in multiple versions are
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the following:
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.IP * 3
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By now there are three different implementations of
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By now there are three different versions of
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.BR stat (2):
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.IR sys_stat ()
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(slot
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@ -583,16 +635,14 @@ refer to the routines
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and
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.IR sys_newuname ().
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.IP *
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In Linux 2.0,
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a new version of
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In Linux 2.0, a new version of
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.BR vm86 (2)
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appeared, with the old and the new kernel routines being named
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.IR sys_vm86old ()
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and
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.IR sys_vm86 ().
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.IP *
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In Linux 2.4,
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a new version of
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In Linux 2.4, a new version of
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.BR getrlimit (2)
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appeared, with the old and the new kernel routines being named
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.IR sys_old_getrlimit ()
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@ -644,14 +694,14 @@ of real-time signals (see
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These system calls supersede the older system calls of the same
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name without the "rt_" prefix.
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.IP *
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It is different with
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.B select (2)
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The
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.BR select (2)
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and
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.BR mmap (2).
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These use five or more parameters, and caused problems the way
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.BR mmap (2)
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system calls use five or more parameters,
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which caused problems the way
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parameter passing on the i386 used to be set up.
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Thus, while
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other architectures have
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Thus, while other architectures have
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.IR sys_select ()
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and
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.IR sys_mmap ()
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@ -668,37 +718,31 @@ parameter block) instead.
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These days passing five parameters
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is not a problem any more, and there is a
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.IR __NR__newselect
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(used by
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libc 6) that corresponds directly to
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.\" (used by libc 6)
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that corresponds directly to
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.IR sys_select ()
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and similarly
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.IR __NR_mmap2.
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.PP
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Two system call numbers,
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.IR __NR__llseek
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and
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.IR __NR__sysctl
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have an additional underscore absent in
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.IR sys_llseek ()
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and
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.IR sys_sysctl ().
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On many platforms, including i386, socket calls are all multiplexed
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through
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.BR socketcall (2)
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and System V IPC calls are multiplexed through
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.BR ipc (2).
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In kernel 2.1.81,
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.BR lchown (2)
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and
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.BR chown (2)
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were swapped; that is,
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.BR lchown (2)
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was added with the semantics that were then current for
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.BR chown (2),
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and the semantics of the latter call were changed to what
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they are today.
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.IR __NR_mmap2 .
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.\" .PP
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.\" Two system call numbers,
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.\" .IR __NR__llseek
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.\" and
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.\" .IR __NR__sysctl
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.\" have an additional underscore absent in
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.\" .IR sys_llseek ()
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.\" and
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.\" .IR sys_sysctl ().
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.\"
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.\" In kernel 2.1.81,
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.\" .BR lchown (2)
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.\" and
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.\" .BR chown (2)
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.\" were swapped; that is,
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.\" .BR lchown (2)
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.\" was added with the semantics that were then current for
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.\" .BR chown (2),
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.\" and the semantics of the latter call were changed to what
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.\" they are today.
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.SH SEE ALSO
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.BR syscall (2),
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.BR unimplemented (2)
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