What are Linux signals?
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:
- Maskable: signals which can be changed or ignored by the user (e.g., Ctrl+C).
- Non-Maskable: signals which cannot be changed or ignored by the user. These typically occur when the user is signaled for non-recoverable hardware errors.
Signals List
The table below contains some common signals and their associated meanings.
| Signal | Description |
|---|---|
| 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). |
First install man-db package to install man pages. For this purpose use the following command:
apt-get install man-db
To get a complete table with a summary of the meaning of each signal, use the following command:
man 7 signal
To test the commands given above, use the terminal provided below:
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