Linux Signal CheatSheet
- PDF Link: cheatsheet-signal-A4.pdf, Category: linux
- Blog URL: https://cheatsheet.dennyzhang.com/cheatsheet-signal-A4
- Related posts: CheatSheet: shell, CheatSheet: SRE/DevOps/Sysadmin, #denny-cheatsheets
1.1 Basic
| Name | Command |
|---|---|
| Signal for interprocess communication | A Kernel notify a process that some condition has occurred. |
kill -l |
List all signals |
| Critical signals | The signals SIGKILL and SIGSTOP cannot be caught, blocked, or ignored. |
SIGKILL, SIGTERM |
Send kill signal to a given process. kill -term $pid, kill -9 $pid |
SIGHUP |
Reload or restart a process. kill -HUP $pid |
SIGHUP |
Terminal warns dependent processes of logout |
SIGINT |
Users wish to interrupt the process |
SIGCHILD |
When a child process terminates, instruct OS to cleanup the resource |
SIGSTOP |
Suspend a process |
SIGALRM |
|
SIGUSR1, SIGUSR2 |
User defined signals |
SIGSTOP vs SIGTSTP |
SIGSTOP can’t be ignored by the targetted process, but SIGTSTP can |
| What happens, when pressing Ctrl-C | Kernal translates the ASCII character(^C) to SIGINT signal |
| Reference | wikipedia: Signal (IPC) |
1.2 Background & Daemons
| Name | Command |
|---|---|
| Suspend process: bring it to background | kill -STOP $pid, Ctrl-z |
| Bring a background process to foreground | fg $JOB_ID |
| List all background jobs | jobs, jobs -l |
| Put a running process to background, and ignore HUP signal | nohup $command & |
| nohup with redirection | nohup $command>foo.out 2>foo.err < /dev/null & |
| Tools to bring process to background and detach signals | nohup, tmux, screen |