A signal is an event generated by the UNIX and Linux systems in response to some condition. Upon receipt of a signal, a process may take action.
A signal is just like an interrupt; when it is generated at the user level, a call is made to the kernel of the OS, which then acts accordingly.
There are two types of signals:
The table below contains some common signals and their associated meanings.
|SIGHUP||Hang-up detected on controlling terminal or death of controlling process.|
|SIGINT||Issued if the user sends an interrupt signal (Ctrl + C).|
|SIGQUIT||Issued if the user sends a quit signal (Ctrl + D).|
|SIGFPE||Issued if an illegal mathematical operation is attempted.|
|SIGKILL||If a process gets this signal, it must quit immediately and will not perform any clean-up operations.|
|SIGTERM||Software termination signal (sent kill by default).|
|SIGALRM||Alarm clock signal (used for timers).|
When executed on the terminal, the command
man 7 signal
shows a complete table with a summary of the meaning of each signal.
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