From Wikipedia, the free encyclopedia
SIGCHLD
| Description |
Child process terminated or stopped |
| Default action |
Ignore the signal |
|
|
SA_SIGINFO macros
|
CLD_EXITED |
child has exited |
CLD_KILLED |
child has terminated abnormally and did not create a core file |
CLD_DUMPED |
child has terminated abnormally and created a core file |
CLD_TRAPPED |
traced child has trapped |
CLD_STOPPED |
child has stopped |
CLD_CONTINUED |
stopped child has continued |
|
On POSIX-compliant platforms, SIGCHLD is the signal sent by computer programs when a child process terminates. The symbolic constant for SIGCHLD is defined in the header file signal.h. Symbolic signal names are used because signal numbers can vary across platforms.
On Linux, SIGCLD is a synonym for SIGCHLD.
[edit] Etymology
SIG is a common prefix for signal names. CHLD and CLD are abbreviations for child.
In Unix, a process can have children, created by fork or similar system calls. When the child terminates a SIGCHLD signal is sent to the parent. By default the signal is ignored and a zombie process is created[1]. The parent must install a handler to act on the signal. Zombies can be avoided on most Unix platforms by explicitly ignoring SIGCHLD[2][3]. This is shown in various languages in the table below. However, installing a signal handler for SIGCHLD and calling wait remain the most portable way to avoid zombies.
| Language |
Syntax |
| C |
signal(SIGCHLD, SIG_IGN); |
| Perl |
$SIG{CHLD} = 'IGNORE'; |
| Python |
signal.signal(signal.SIGCHLD, signal.SIG_IGN) |
| PHP |
pcntl_signal(SIGCHLD, SIG_IGN); |
[edit] References
- ^ Advanced Programming in the UNIX Environment - W. Stevens
- ^ perlipc - perldoc.perl.org
- ^
sigaction(3): examine and change a signal action – Linux man page
