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Signals in Linux
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Introduction
Signals are used to interact between processes and can occur at anytime, typically they are kill signals however processes can opt to handle them programatically unless they are SIGKILL or SIGSTOP signals.
List Of Available Signals
Table of signals
| SIGNAL | VALUE | DEFAULT ACTION | POSIX? | MEANING |
|---|---|---|---|---|
| SIGHUP | 1 | Terminate | Yes | Hangup detected on controlling terminal or death of controlling process |
| SIGINT | 2 | Terminate | Yes | Interrupt from keyboard |
| SIGQUIT | 3 | Core dump | Yes | Quit from keyboard |
| SIGILL | 4 | Core dump | Yes | Illegal instruction |
| SIGTRAP | 5 | Core dump | No | Trace/breakpoint trap for debugging |
| SIGABTR SIGIOT | 6 | Core dump | Yes | Abnormal termination |
| SIGBUS | 7 | Core dump | Yes | Bus error |
| SIGFPE | 8 | Core dump | Yes | Floating point exception |
| SIGKILL | 9 | Terminate | Yes | Kill signal (cannot be caught or ignored) |
| SIGUSR1 | 10 | Terminate | Yes | User-defined signal 1 |
| SIGSEGV | 11 | Core dump | Yes | Invalid memory reference |
| SIGUSR2 | 12 | Terminate | Yes | User-defined signal 2 |
| SIGPIPE | 13 | Terminate | Yes | Broken pipe: write to pipe with no readers |
| SIGALRM | 14 | Terminate | Yes | Timer signal from alarm |
| SIGTERM | 15 | Terminate | Yes | Process termination |
| SIGSTKFLT | 16 | Terminate | No | Stack fault on math co-processor |
| SIGCHLD | 17 | Ignore | Yes | Child stopped or terminated |
| SIGCONT | 18 | Continue | Yes | Continue if stopped |
| SIGSTOP | 19 | Stop | Yes | Stop process (can not be caught or ignored) |
| SIGTSTP | 20 | Stop | Yes | Stop types at tty |
| SIGTTIN | 21 | Stop | Yes | Background process requires tty input |
| SIGTTOU | 22 | Stop | Yes | Background process requires tty output |
| SIGURG | 23 | Ignore | No | Urgent condition on socket (4.2 BSD) |
| SIGXCPU | 24 | Core dump | Yes | CPU time limit exceeded (4.2 BSD) |
| SIGXFSZ | 25 | Core dump | Yes | File size limit exceeded (4.2 BSD) |
| SIGVTALRM | 26 | Terminate | No | Virtual alarm clock (4.2 BSD) |
| SIGPROF | 27 | Terminate | No | Profile alarm clock (4.2 BSD) |
| SIGWINCH | 28 | Ignore | No | Window resize signal (4.3 BSD, Sun) |
| SIGIO SIGPOLL | 29 | Terminate | No | I/O now possible (4.2 BSD) (System V) |
| SIGPWR | 30 | Terminate | No | Power Failure (System V) |
| SIGSYS SIGUNUSED | 31 | Terminate | No | Bad System Called. Unused signal |