LINUX System Call
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
1 exit terminate the current process kernel/exit.c
2 fork create a child process arch/i386/kernel/process.c
3 read read from a file descriptor fs/read_write.c
4 write write to a file descriptor fs/read_write.c
5 open open a file or device fs/open.c
6 close close a file descriptor fs/open.c
7 waitpid wait for process termination kernel/exit.c
8 creat create a file or device ("man 2 open" for information) fs/open.c
9 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 permissions of 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
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 execut ion 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/so cket.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
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_interval 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 tomodules 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