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() or 0.

The raise() system call sends a signal to the executing process or thread. The signal to be sent is specified by sig and is either one from the list given in signal() or 0. In a single-threaded process the effect of the raise() function is equivalent to calling

kill(getpid(), sig);.

When used in a multithreaded program, the raise() function sends the signal specified by sig to the executing thread. The effect of the raise() function is equivalent to calling

pthread_kill (pthread_self(), sig);.

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 sending process 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 sending process does not have the 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.

Security Restrictions

Some or all of the actions associated with this system call are subject to compartmental restrictions. See compartments(5) for more information about compartmentalization on systems that support that feature. Compartmental restrictions can be overridden if the process possesses the PRIV_COMMALLOWED privilege (COMMALLOWED). Processes owned by the superuser may not have this privilege. Processes owned by any user may have this privilege, depending on system configuration.

Some or all of the actions associated with this system call require the PRIV_OWNER (OWNER) and/or the PRIV_REBOOT (REBOOT) privileges. Processes owned by the superuser will have these privileges. Processes owned by other users may have privilege(s), depending on system configuration. See privileges(5) for more information about privileged access on systems that support fine-grained privileges.

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 that of the initialization process (also known as init).
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 the following value.

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