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LINUX System Call Quick Reference

Jialong He

Jialong_he@bigfoot.com

http://www.bigfoot.com/jialong_he

Introduction

System call is the services provided by Linux kernel. In C programming, it often uses functions defined in libc

which provides a wrapper for many system calls. Manual page section 2 provides more information about

system calls. To get an overview, use “man 2 intro” in a command shell.

It is also possible to invoke syscall() function directly. Each system call has a function number defined in

<syscall.h>or <unistd.h>. Internally, system call is invokded by software interrupt 0x80 to transfer control to

the kernel. System call table is defined in Linux kernel source file “arch/i386/kernel/entry.S ”.

System Call Example

#include <syscall.h>

#include <unistd.h>

#include <stdio.h>

#include <sys/types.h>

int main(void) {

long ID1, ID2;

/*-----------------------------*/

/* direct system call */

/* SYS_getpid (func no. is 20) */

/*-----------------------------*/

ID1 = syscall(SYS_getpid);

printf ("syscall(SYS_getpid)=%ld\n", ID1);

/*-----------------------------*/

/* "libc" wrapped system call */

/* SYS_getpid (Func No. is 20) */

/*-----------------------------*/

ID2 = getpid();

printf ("getpid()=%ld\n", ID2);

return(0);

}

System Call Quick Reference

No Func Name Description

Source

exit

terminate the current process

kernel/exit.c

fork

create a child process

arch/i386/kernel/process.c

read

read from a file descriptor

fs/read_write.c

write

write to a file descriptor

fs/read_write.c

open

open a file or device

fs/open.c

close

close a file descriptor

fs/open.c

waitpid

wait for process termination

kernel/exit.c

creat

create a file or device ("man 2 open" for

information)

fs/open.c

link

make a new name for a file

fs/namei.c

10 unlink

delete a name and possibly the file it refers to

fs/namei.c

11 execve

execute program

arch/i386/kernel/process.c

12 chdir

change working directory

fs/open.c

13 time

get time in seconds

kernel/time.c

14 mknod

create a special or ordinary file

fs/namei.c

15 chmod

change permissionsof a file

fs/open.c

16 lchown

change ownership of a file

fs/open.c

18 stat

get file status

fs/stat.c

19 lseek

reposition read/write file offset

fs/read_write.c

20 getpid

get process identification

kernel/sched.c

21 mount

mount filesystems

fs/super.c

22 umount

unmount filesystems

fs/super.c

23 setuid

set real user ID

kernel/sys.c

24 getuid

get real user ID

kernel/sched.c

25 stime

set system time and date

kernel/time.c

26 ptrace

allows a parent process to control the execution of

a child process

arch/i386/kernel/ptrace.c

27 alarm

set an alarm clock for delivery of a signal

kernel/sched.c

28 fstat

get file status

fs/stat.c

29 pause

suspend process until signal

arch/i386/kernel/sys_i386.c

30 utime

set file access and modification times

fs/open.c

33 access

check user's permissions for a file

fs/open.c

34 nice

change process priority

kernel/sched.c

36 sync

update the super block

fs/buffer.c

37 kill

send signal to a process

kernel/signal.c

38 rename

change the name or location of a file

fs/namei.c

39 mkdir

create a directory

fs/namei.c

40 rmdir

remove a directory

fs/namei.c

41 dup

duplicate an open file descriptor

fs/fcntl.c

42 pipe

create an interprocess channel

arch/i386/kernel/sys_i386.c

43 times

get process times

kernel/sys.c

45 brk

change the amount of space allocated for the

calling process's data segment

mm/mmap.c

46 setgid

set real group ID

kernel/sys.c

47 getgid

get real group ID

kernel/sched.c

48 sys_signal

ANSI C signal handling

kernel/signal.c

49 geteuid

get effective user ID

kernel/sched.c

50 getegid

get effective group ID

kernel/sched.c

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51 acct

enable or disable process accounting

kernel/acct.c

52 umount2

unmount a file system

fs/super.c

54 ioctl

control device

fs/ioctl.c

55 fcntl

file control

fs/fcntl.c

56 mpx

(unimplemented)

57 setpgid

set process group ID

kernel/sys.c

58 ulimit

(unimplemented)

59 olduname

obsolete uname system call

arch/i386/kernel/sys_i386.c

60 umask

set file creation mask

kernel/sys.c

61 chroot

change root directory

fs/open.c

62 ustat

get file system statistics

fs/super.c

63 dup2

duplicate a file descriptor

fs/fcntl.c

64 getppid

get parent process ID

kernel/sched.c

65 getpgrp

get the process group ID

kernel/sys.c

66 setsid

creates a session and sets the process group ID

kernel/sys.c

67 sigaction

POSIX signal handling functions

arch/i386/kernel/signal.c

68 sgetmask

ANSI C signal handling

kernel/signal.c

69 ssetmask

ANSI C signal handling

kernel/signal.c

70 setreuid

set real and effective user IDs

kernel/sys.c

71 setregid

set real and effective group IDs

kernel/sys.c

72 sigsuspend

install a signal mask and suspend caller until

signal

arch/i386/kernel/signal.c

73 sigpending

examine signals that are blocked and pending

kernel/signal.c

74 sethostname

set hostname

kernel/sys.c

75 setrlimit

set maximum system resource con sumption

kernel/sys.c

76 getrlimit

get maximum system resource con sumption

kernel/sys.c

77 getrusage

get maximum system resource con sumption

kernel/sys.c

78 gettimeofday

get the date and time

kernel/time.c

79 settimeofday

set the date and time

kernel/time.c

80 getgroups

get list of supplementary group IDs

kernel/sys.c

81 setgroups

set list of supplementary group IDs

kernel/sys.c

82 old_select

sync. I/O multiplexing

arch/i386/kernel/sys_i386.c

83 symlink

make a symbolic link to a file

fs/namei.c

84 lstat

get file status

fs/stat.c

85 readlink

read the contents of a symbolic link

fs/stat.c

86 uselib

select shared library

fs/exec.c

87 swapon

start swapping to file/device

mm/swapfile.c

88 reboot

reboot or enable/disable Ctrl-Alt-Del

kernel/sys.c

89 old_readdir

read directory entry

fs/readdir.c

90 old_mmap

map pages of memory

arch/i386/kernel/sys_i386.c

91 munmap

unmap pages of memory

mm/mmap.c

92 truncate

set a file to a specified length

fs/open.c

93 ftruncate

set a file to a specified length

fs/open.c

94 fchmod

change access permission mode of file

fs/open.c

95 fchown

change owner and group of a file

fs/open.c

96 getpriority

get program scheduling priority

kernel/sys.c

97 setpriority

set program scheduling priority

kernel/sys.c

98 profil

execution time profile

99 statfs

get file system statistics

fs/open.c

100 fstatfs

get file system statistics

fs/open.c

101 ioperm

set port input/output permissions

arch/i386/kernel/ioport.c

102 socketcall

socket system calls

net/socket.c

103 syslog

read and/or clear kernel message ring buffer

kernel/printk.c

104 setitimer

set value of interval timer

kernel/itimer.c

105 getitimer

get value of interval timer

kernel/itimer.c

106 sys_newstat

get file status

fs/stat.c

107 sys_newlstat

get file status

fs/stat.c

108 sys_newfstat

get file status

fs/stat.c

109 olduname

get name and information about current kernel

arch/i386/kernel/sys_i386.c

110 iopl

change I/O privilege level

arch/i386/kernel/ioport.c

111 vhangup

virtually hangup the current tty

fs/open.c

112 idle

make process 0 idle

arch/i386/kernel/process.c

113 vm86old

enter virtual 8086 mode

arch/i386/kernel/vm86.c

114 wait4

wait for process termination, BSD style

kernel/exit.c

115 swapoff

stop swapping to file/device

mm/swapfile.c

116 sysinfo

returns information on overall system statistics

kernel/info.c

117 ipc

System V IPC system calls

arch/i386/kernel/sys_i386.c

118 fsync

synchronize a file's complete in-core state with that

on disk

fs/buffer.c

119 sigreturn

return from signal handler and cleanup stack

frame

arch/i386/kernel/signal.c

120 clone

create a child process

arch/i386/kernel/process.c

121 setdomainname

set domain name

kernel/sys.c

122 uname

get name and information about current kernel

kernel/sys.c

123 modify_ldt

get or set ldt

arch/i386/kernel/ldt.c

124 adjtimex

tune kernel clock

kernel/time.c

125 mprotect

set protection of memory mapping

mm/mprotect.c

126 sigprocmask

POSIX signal handling functions

kernel/signal.c

127 create_module

create a loadable module entry

kernel/module.c

128 init_module

initialize a loadable module entry

kernel/module.c

129 delete_module

delete a loadable module entry

kernel/module.c

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130 get_kernel_syms

retrieve exported kernel and module symbols

kernel/module.c

131 quotactl

manipulate disk quotas

fs/dquot.c

132 getpgid

get process group ID

kernel/sys.c

133 fchdir

change working directory

fs/open.c

134 bdflush

start, flush, or tune buffer-dirty-flush daemon

fs/buffer.c

135 sysfs

get file system type information

fs/super.c

136 personality

set the process execution domain

kernel/exec_domain.c

137 afs_syscall

(unimplemented)

138 setfsuid

set user identity used for file system checks

kernel/sys.c

139 setfsgid

set group identity used for file system checks

kernel/sys.c

140 sys_llseek

move extended read/write file pointer

fs/read_write.c

141 getdents

read directory entries

fs/readdir.c

142 select

sync. I/O multiplexing

fs/select.c

143 flock

apply or remove an advisory lock on an open file

fs/locks.c

144 msync

synchronize a file with a memory map

mm/filemap.c

145 readv

read data into multiple buffers

fs/read_write.c

146 writev

write data into multiple buffers

fs/read_write.c

147 sys_getsid

get process group ID of session leader

kernel/sys.c

148 fdatasync

synchronize a file's in-core data with that on disk

fs/buffer.c

149 sysctl

read/write system parameters

kernel/sysctl.c

150 mlock

lock pages in memory

mm/mlock.c

151 munlock

unlock pages in memory

mm/mlock.c

152 mlockall

disable paging for calling process

mm/mlock.c

153 munlockall

reenable paging for calling process

mm/mlock.c

154 sched_setparam

set scheduling parameters

kernel/sched.c

155 sched_getparam

get scheduling parameters

kernel/sched.c

156 sched_setscheduler set scheduling algorithm parameters

kernel/sched.c

157 sched_getscheduler get scheduling algorithm parameters

kernel/sched.c

158 sched_yield

yield the processor

kernel/sched.c

159

sched_get_priority_

max

get max static priority range

kernel/sched.c

160

sched_get_priority_

min

get min static priority range

kernel/sched.c

161

sched_rr_get_inter

val

get the SCHED_RR interval for the named process

kernel/sched.c

162 nanosleep

pause execution for a specified time (nano seconds) kernel/sched.c

163 mremap

re-map a virtual memory address

mm/mremap.c

164 setresuid

set real, effective and saved user or group ID

kernel/sys.c

165 getresuid

get real, effective and saved user or group ID

kernel/sys.c

166 vm86

enter virtual 8086 mode

arch/i386/kernel/vm86.c

167 query_module

query the kernel for various bits pertain ing to

modules

kernel/module.c

168 poll

wait for some event on a file descriptor

fs/select.c

169 nfsservctl

syscall interface to kernel nfs daemon

fs/filesystems.c

170 setresgid

set real, effective and saved user or group ID

kernel/sys.c

171 getresgid

get real, effective and saved user or group ID

kernel/sys.c

172 prctl

operations on a process

kernel/sys.c

173 rt_sigreturn

arch/i386/kernel/signal.c

174 rt_sigaction

kernel/signal.c

175 rt_sigprocmask

kernel/signal.c

176 rt_sigpending

kernel/signal.c

177 rt_sigtimedwait

kernel/signal.c

178 rt_sigqueueinfo

kernel/signal.c

179 rt_sigsuspend

arch/i386/kernel/signal.c

180 pread

read from a file descriptor at a given offset

fs/read_write.c

181 sys_pwrite

write to a file descriptor at a given offset

fs/read_write.c

182 chown

change ownership of a file

fs/open.c

183 getcwd

Get current working directory

fs/dcache.c

184 capget

get process capabilities

kernel/capability.c

185 capset

set process capabilities

kernel/capability.c

186 sigaltstack

set/get signal stack context

arch/i386/kernel/signal.c

187 sendfile

transfer data between file descriptors

mm/filemap.c

188 getpmsg

(unimplemented)

189 putpmsg

(unimplemented)

190 vfork

create a child process and block parent

arch/i386/kernel/process.c