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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 
  1. include <syscall.h>
  2. include <unistd.h>
  3. include <stdio.h>
  4. 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 old uname 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 s tate 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_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