First the signals described in the original POSIX.1-1990 standard.
| Signal | Value | Action | Comment |
|---|---|---|---|
| SIGHUP | 1 | Term | Hangup detected on controlling terminal or death of controlling process |
| SIGINT | 2 | Term | Interrupt from keyboard |
| SIGQUIT | 3 | Core | Quit from keyboard |
| SIGILL | 4 | Core | Illegal Instruction |
| SIGABRT | 6 | Core | Abort signal from abort(3) |
| SIGFPE | 8 | Core | Floating point exception |
| SIGKILL | 9 | Term | Kill signal |
| SIGSEGV | 11 | Core | Invalid memory reference |
| SIGPIPE | 13 | Term | Broken pipe: write to pipe with no readers |
| SIGALRM | 14 | Term | Timer signal from alarm(2) |
| SIGTERM | 15 | Term | Termination signal |
| SIGUSR1 | 30,10,16 | Term | User-defined signal 1 |
| SIGUSR2 | 31,12,17 | Term | User-defined signal 2 |
| SIGCHLD | 20,17,18 | Ign | Child stopped or terminated |
| SIGCONT | 19,18,25 | Cont | Continue if stopped |
| SIGSTOP | 17,19,23 | Stop | Stop process |
| SIGTSTP | 18,20,24 | Stop | typed at terminal |
| SIGTTIN | 21,21,26 | Stop | Terminal input for background process |
| SIGTTOU | 22,22,27 | Stop | Terminal output for background process |
The signals SIGKILL and SIGSTOP cannot be caught, blocked, or ignored. | |||
| Next the signals not in the POSIX.1-1990 standard but described in | |||
| SUSv2 and POSIX.1-2001. |
| Signal | Value | Action | Comment |
|---|---|---|---|
| SIGBUS | 10,7,10 | Core | Bus error (bad memory access) |
| SIGPOLL | Term | Pollable event (Sys V). Synonym for SIGIO | |
| SIGPROF | 27,27,29 | Term | Profiling timer expired |
| SIGSYS | 12,31,12 | Core | Bad argument to routine (SVr4) |
| SIGTRAP | 5 | Core | Trace/breakpoint trap |
| SIGURG | 16,23,21 | Ign | Urgent condition on socket (4.2BSD) |
| SIGVTALRM | 26,26,28 | Term | Virtual alarm clock (4.2BSD) |
| SIGXCPU | 24,24,30 | Core | CPU time limit exceeded (4.2BSD) |
| SIGXFSZ | 25,25,31 | Core | File size limit exceeded (4.2BSD) |
| Up to and including Linux 2.2, the default behavior for SIGSYS, SIGX‐CPU, SIGXFSZ, and (on architectures other than SPARC and MIPS) SIGBUS was to terminate the process (without a core dump). (On some other UNIX systems the default action for SIGXCPU and SIGXFSZ is to terminate the process without a core dump.) Linux 2.4 conforms to the POSIX.1-2001 requirements for these signals, terminating the process with a core dump. |
Next various other signals.
| Signal | Value | Action | Comment |
|---|---|---|---|
| SIGIOT | 6 | Core | IOT trap. A synonym for SIGABRT |
| SIGEMT | 7,-,7 | Term | |
| SIGSTKFLT | -,16,- | Term | Stack fault on coprocessor (unused) |
| SIGIO | 23,29,22 | Term | I/O now possible (4.2BSD) |
| SIGCLD | -,-,18 | Ign | A synonym for SIGCHLD |
| SIGPWR | 29,30,19 | Term | Power failure (System V) |
| SIGINFO | 29,-,- | A synonym for SIGPWR | |
| SIGLOST | -,-,- | Term | File lock lost (unused) |
| SIGWINCH | 28,28,20 | Ign | Window resize signal (4.3BSD, Sun) |
| SIGUNUSED | -,31,- | Core | Synonymous with SIGSYS |
| (Signal 29 is SIGINFO / SIGPWR on an alpha but SIGLOST on a sparc.) |
SIGEMT is not specified in POSIX.1-2001, but nevertheless appears on most other UNIX systems, where its default action is typically to ter‐ minate the process with a core dump.
SIGPWR (which is not specified in POSIX.1-2001) is typically ignored by default on those other UNIX systems where it appears.
SIGIO (which is not specified in POSIX.1-2001) is ignored by default on several other UNIX systems.
Where defined, SIGUNUSED is synonymous with SIGSYS on most architec‐ tures.