kill(2)

NAME

kill(), raise() — send a signal to a process or a group of processes

SYNOPSIS

#include <signal.h>

int kill(pid_t pid, int sig);

int raise(int sig);

DESCRIPTION

The kill() system call sends a signal to a process or a group of processes, as specified by pid. The signal to be sent is specified by sig and is either one from the list given in signal(2), or 0.

The raise() system call sends a signal to the executing program. The signal to be sent is specified by sig and is either one from the list given in signal(2), or 0.

If sig is 0 (the null signal), error checking is performed but no signal is actually sent. This can be used to check the validity of pid.

The real or effective user ID of the sending process must match the real or saved user ID of the receiving process unless the effective user ID of the sending process is a user who has appropriate privileges.

As a single special case, the continue signal SIGCONT can be sent to any process that is a member of the same session as the sending process.

The value KILL_ALL_OTHERS is defined in the file <sys/signal.h> and is guaranteed not to be the ID of any process in the system or the negation of the ID of any process in the system.

If pid is greater than zero and not equal to KILL_ALL_OTHERS, sig is sent to the process whose process ID is equal to pid. pid can equal 1 unless sig is SIGKILL or SIGSTOP.

If pid is 0, sig is sent to all processes excluding special system processes whose process group ID is equal to the process group ID of the sender.

If pid is -1 and the effective user ID of the sender is not a user who has appropriate privileges. sig is sent to all processes excluding special system processes whose real or saved user ID is equal to the real or effective user ID of the sender.

If pid is -1 and the effective user ID of the sender is a user who has appropriate privileges, sig is sent to all processes excluding special system processes.

If pid is KILL_ALL_OTHERS, kill() behaves much as when pid is equal to -1, except that sig is not sent to the calling process.

If pid is negative but not -1 or KILL_ALL_OTHERS, sig is sent to all processes (excluding special system processes) whose process group ID is equal to the absolute value of pid, and whose real and/or effective user ID meets the constraints described above for matching user IDs.

RETURN VALUE

Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.

ERRORS

If kill() fails, no signal is sent. errno is set to one of the following values.

[EINVAL]: sig is neither a valid signal number nor zero.
[EINVAL]: sig is SIGKILL or SIGSTOP and pid is 1 (process 1).
[EPERM]: The user ID of the sending process is not a user who has appropriate privileges and its real or effective user ID does not match the real or saved user ID of the receiving process.
[EPERM]: The sending and receiving processes are not in the same session and the real or effective user ID does not match the real or saved user ID of the receiving process.
[ESRCH]: No process or process group can be found corresponding to that specified by pid.

If raise() fails, no signal is sent. errno is set to one of the following values.

[EINVAL]: sig is neither a valid signal number nor zero.

APPLICATION USAGE

Threads Considerations

kill() can be used to post signals to another process but cannot be used to post signals to a specific thread in another process. For information on posting signals to specific threads within the same process, see pthread_kill(3T).

LWP (Lightweight Processes) Considerations

Signals cannot be posted to specific LWPs in another process.

AUTHOR

kill() was developed by HP, AT&T, and the University of California, Berkeley.

STANDARDS CONFORMANCE

kill(): AES, SVID2, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1

raise(): AES, SVID3, XPG4, ANSI C