Each signal has a default action associated with it, which determines how the process behaves when it is delivered to the signal.
Some of the actions are −
- Terminate the process.
- Ignore the signal.
- Dump core. This creates a file called process core dump.
- Stop the process.
- Continue a stopped process
How to send a signal to a program or script?
- CTRL+C >Send SIGINT
- kill -signal <PID>
You can check all signals type with “kill -l” command.
# kill -l 1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP 6) SIGABRT 7) SIGEMT 8) SIGFPE 9) SIGKILL 10) SIGBUS 11) SIGSEGV 12) SIGSYS 13) SIGPIPE 14) SIGALRM 15) SIGTERM 16) SIGUSR1 17) SIGUSR2 18) SIGCHLD 19) SIGPWR 20) SIGWINCH 21) SIGURG 22) SIGIO 23) SIGSTOP 24) SIGTSTP 25) SIGCONT 26) SIGTTIN 27) SIGTTOU 28) SIGVTALRM 29) SIGPROF 30) SIGXCPU 31) SIGXFSZ 32) SIGWAITING 33) SIGLWP 34) SIGFREEZE 35) SIGTHAW 36) SIGCANCEL 37) SIGLOST 38) SIGXRES 41) SIGRTMIN 42) SIGRTMIN+1 43) SIGRTMIN+2 44) SIGRTMIN+3 45) SIGRTMAX-3 46) SIGRTMAX-2 47) SIGRTMAX-1 48) SIGRTMAX
Use “trap” command to;
- cleanup temporary files
- Ignore signals
How to use “trap” signals?
With trap command, you can ignore signals or clean up temporary files.
#trap command signals
Example:trap “rm -f $WORKDIR/tmp1 $WORKDIR/tmp2 ; exit” 2 //user send interrupts execution of the program,this two files ‘ll be removed.
SIGHUP | 1 | Exit | Hangup |
SIGINT | 2 | Exit | Interrupt |
SIGQUIT | 3 | Core | Quit |
SIGILL | 4 | Core | Illegal Instruction |
SIGTRAP | 5 | Core | Trace/Breakpoint Trap |
SIGABRT | 6 | Core | Abort |
SIGEMT | 7 | Core | Emulation Trap |
SIGFPE | 8 | Core | Arithmetic Exception |
SIGKILL | 9 | Exit | Killed |
SIGBUS | 10 | Core | Bus Error |
SIGSEGV | 11 | Core | Segmentation Fault |
SIGSYS | 12 | Core | Bad System Call |
SIGPIPE | 13 | Exit | Broken Pipe |
SIGALRM | 14 | Exit | Alarm Clock |
SIGTERM | 15 | Exit | Terminated |
SIGUSR1 | 16 | Exit | User Signal 1 |
SIGUSR2 | 17 | Exit | User Signal 2 |
SIGCHLD | 18 | Ignore | Child Status |
SIGPWR | 19 | Ignore | Power Fail/Restart |
SIGWINCH | 20 | Ignore | Window Size Change |
SIGURG | 21 | Ignore | Urgent Socket Condition |
SIGPOLL | 22 | Ignore | Socket I/O Possible |
SIGSTOP | 23 | Stop | Stopped (signal) |
SIGTSTP | 24 | Stop | Stopped (user) |
SIGCONT | 25 | Ignore | Continued |
SIGTTIN | 26 | Stop | Stopped (tty input) |
SIGTTOU | 27 | Stop | Stopped (tty output) |
SIGVTALRM | 28 | Exit | Virtual Timer Expired |
SIGPROF | 29 | Exit | Profiling Timer Expired |
SIGXCPU | 30 | Core | CPU time limit exceeded |
SIGXFSZ | 31 | Core | File size limit exceeded |
SIGWAITING | 32 | Ignore | All LWPs blocked |
SIGLWP | 33 | Ignore | Virtual Interprocessor Interrupt for Threads Library |
SIGAIO | 34 | Ignore | Asynchronous I/O |