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Written by Oleksandr Gavenko (AKA gavenkoa), compiled on 2017-01-30 from rev ccaa2f364422+.

Process signal

Send signal to process

$ kill -s NAME PID

Under C you can use kill(2) system call which will send the specified signal to the process, if permissions allow, or raise(3) library function, which sends the specified signal to the current process.

List of signals

$ kill --list $ kill -l # short variant

See

http://en.wikipedia.org/wiki/Unix_signals

Signal descriptions

SIGHUP 1

Hangup. Type: notification, can be handled.

Sent when assigned to process terminal closed.

nohup(1) utility used as a wrapper to start a program and make it immune to SIGHUP.

The default action on POSIX-compliant systems is an abnormal termination.

Demon used this signal as commant to reread config file.

SIGINT

Interrupt. Ctrl-C. Type: control, can be handled.

Signal sent to a process by its controlling terminal when a user wishes to interrupt the process.

By default, this causes the process to terminate.

SIGQUIT 3

Quit. Ctrl-. Type: control.

Signal sent to a process by its controlling terminal when the user requests that the process dump core.

By default, this causes the process to terminate and produce a memory core dump.

Java dump thread traces to stdout.

SIGILL 4

Illegal instruction. Type: exception, can not be handled.

Signal sent to a process when it attempts to execute a malformed, unknown, or privileged instruction.

SIGTRAP 5

Trace trap. Type: debug, can be handled.

Signal sent to a process when a condition arises that a debugger has requested to be informed of.

By default this causes abnormal termination of the process.

SIGABRT 6

Type: control, can be handled.

Signal sent to a computer program to tell it to abort, ie terminate.

SIGABRT is sent by the process to itself when it calls the abort libc function. It is used when an assertion fails.

By default this causes abnormal termination of the process.

SIGEMT 7

Emt instruction.

SIGFPE 8

Floating point exception. Type: exception, can be handled.

Signal sent to a process when it performs an erroneous arithmetic operation (like division by zero).

By default cause a core dump and a program exit.

SIGKILL 9

Kill. Type: control, can not be handled.

Signal sent to a process to cause it to terminate immediately.

Zombie processes cannot be killed since they are already dead and waiting for their parent processes to reap them.

Processes that are in the blocked state will not die until they wake up again.

SIGBUS 10

Bus error. Type: exception, can not be handled.

Signal sent to a process when it causes a bus error.

By default this causes abnormal termination of the process.

SIGSEGV 11

Segmentation violation. Type: exception.

Signal sent to a process when it makes an invalid memory reference, or segmentation fault.

By default cause a core dump and a program exit.

SIGSYS 12

Bad argument to system call. Type: exception.

By default this causes abnormal termination of the process.

SIGPIPE 13

Write on a pipe with no one to read it. Type: notification.

Signal sent to a process when it attempts to write to a pipe without a process connected to the other end.

This causes the process to terminate, which is convenient when constructing shell pipelines.

SIGALRM 14

Alarm clock. Type: notification.

Signal sent to a process when a time limit has elapsed.

By default this causes abnormal termination of the process.

SIGTERM 15

Software termination signal. Type: control.

Signal sent to a process to request its termination.

It causes the termination of a process, but unlike the SIGKILL signal, it can be caught and interpreted (or ignored) by the process.

SIGTERM is akin to asking a process to terminate nicely, allowing cleanup and closure of files. For this reason, on many Unix systems during shutdown, init issues SIGTERM to all processes that are not essential to powering off, waits a few seconds, and then issues SIGKILL to forcibly terminate any such processes that remain.

By default kill(1) send to process SIGTERM signal.

SIGURG 16

Urgent condition on IO channel. Type: notification.

By default this signal ignored.

SIGSTOP 17

Signal sent to a process to stop it for later resumption. Type: control.

SIGSTOP cannot be caught or ignored.

Usually SIGSTOP and SIGCONT are used for job control in the Unix shell.

SIGTSTP 18

Stop signal from tty. Ctrl-Z. Type: control.

By default, this causes the process to suspend execution.

SIGCONT 19

Continue a stopped process. Type: control.

Signal sent to restart a process previously paused by the SIGSTOP or SIGTSTP signal.

SIGCHLD 20

To parent on child stop or exit. Type: notification.

By default the signal is simply ignored. In C:

signal(SIGCHLD, SIG_IGN);

Parent can invoke wait(1) otherwise children stay zombie.

SIGTTIN 21

Signal sent to a process when it attempts to read from the tty while in the background.

Daemons do not have controlling terminals and should never receive this signal.

By default this causes suspends of the process.

SIGTTOU 22

Signal sent to a process when it attempts to write to the tty while in the background.

Daemons do not have controlling terminals and should never receive this signal.

By default this causes suspends of the process.

SIGPOLL 23

System V name for SIGIO. Type: notification.

Signal sent to a process when an asynchronous I/O event occurs.

By default this causes abnormal termination of the process.

SIGXCPU 24

Exceeded CPU time limit. Type: notification.

By default this causes abnormal termination of the process.

SIGXFSZ 25

Exceeded file size limit as determined by the ulimit system call and shell builtin. Type: notification.

By default this causes abnormal termination of the process.

SIGVTALRM 26

Virtual time alarm. Type: notification.

Signal sent to a process when a time limit has elapsed.

By default this causes abnormal termination of the process.

SIGPROF 27

Profiling time alarm. Type: debug.

Signal sent to a process when the profiling timer expires.

By default this causes abnormal termination of the process.

SIGWINCH 28

Window changed. Type: notification.

Signal sent to a process when its controlling terminal changes size.

By default this signal ignored.

SIGLOST 29

Signal sent to process when a file lock is lost. This may occur, for example, when an NFS server reboots and forgets about a file lock.

By default this causes abnormal termination of the process.

SIGUSR1 30

User defined signal 1. Type: user defined.

By default this causes abnormal termination of the process.

SIGUSR2 31

User defined signal 2. Type: user defined.

By default this causes abnormal termination of the process.