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signal(4) Kernel Interfaces Manual signal(4) NAME signal, signal.h - Contains definitions and variables used by signal functions DESCRIPTION The /usr/include/signal.h file defines the signals described in the following table. tab(@); lfHB cfHB lfHB l c lw(3.0i) . _ Signal@Number@Meaning _ SIGHUP@1@Hangup. SIGINT@2@Interrupt. SIGQUIT@3@Quit. (1) SIG- ILL@4@Invalid instruction (not reset when caught). (1) SIGTRAP@5@Trace trap (not reset when caught). (1) SIGABRT@6@End process (see the abort() function). (1) SIGEMT@7@EMT instruction. SIGFPE@8@Arithmetic exception, integer divide by 0 (zero), @@or floating-point exception. (1) SIGKILL@9@Kill (cannot be caught or ignored). SIGBUS@10@Specifica- tion exception. (1) SIGSEGV@11@Segmentation violation. (1) SIGSYS@12@Invalid parameter to system call. (1) SIGPIPE@13@Write on a pipe when there is no process to read it. SIGALRM@14@Alarm clock. SIGTERM@15@Software termination signal. SIGURG@16@Urgent condition on I/O channel. (2) SIGSTOP@17@Stop (cannot be caught or ignored). (3) SIGTSTP@18@Interactive stop. (3) SIGCONT@19@Continue the process if stopped. (4) SIGCHLD@20@To parent on child stop or exit. (2) SIGT- TIN@21@Background read attempted from control terminal. (3) SIGT- TOU@22@Background write attempted from control terminal. (3) SI- GIO@23@Input/Output possible or completed. (2) SIGXCPU@24@CPU time limit exceeded (see the setrlimit() function). SIGXFSZ@25@File size limit exceeded (see the setrlimit() function). SIGVTALRM@26@Virtual time alarm (see the setitimer() function). SIGPROF@27@Profiling time alarm (see the setitimer() function). SIGWINCH@28@Window size change. (2) SIGINFO@29@Information request. (2) SIGUSR1@30@User-defined signal 1. SIGUSR2@31@User-defined signal 2. Notes to table: Default action includes creating a core dump file. Default action is to ignore these signals. Default action is to stop the process receiv- ing these signals. Default action is to restart or continue the process receiving these signals. The three types of actions that can be associated with a signal: SIG_DFL, SIG_IGN, or a pointer to a function are described as follows: Default action: signal-specific default action. Except for those signal numbers marked with a (2), (3), or (4), the default action for a signal is to end the receiving process with all of the consequences described in the _exit() system call. In addition, a memory image file is created in the current directory of the receiving process if the signal parameter is one for which a superscript 1 appears in the preceding list and the following conditions are met: The effective user ID and the real user ID of the receiving process are equal. An ordinary file named core exists in the current directory and is writable, or it can be created. If the file must be created, it will have the following properties: The access permission code 0600, modi- fied by the file creation mask (see the umask() function). A file owner ID that is the same as the effective user ID of the receiving process. A file group ID that is inherited from the containing directory (if the file system is mounted grpid) or from the owning process (if the file system is mounted nogrpid). For signal numbers marked with a superscript 4, the default ac- tion is to restart the receiving process if it is stopped, or to continue execution of the receiving process. For signal numbers marked with a superscript 3, the default ac- tion is to stop the execution of the receiving process temporar- ily. When a process stops, a SIGCHLD signal is sent to its par- ent process, unless the parent process has set the SA_NOCLDSTOP bit. While a process is stopped, any additional signals that are sent to the process are not delivered until the process is con- tinued. An exception to this is SIGKILL, which always terminates the receiving process. Another exception is SIGCONT, which al- ways causes the receiving process to restart or continue run- ning. A process whose parent has ended shall be sent a SIGKILL signal if the SIGTSTP, SIGTTIN, or SIGTTOU signals are generated for that process. For signal numbers marked with a superscript 2, the default ac- tion is to ignore the signal. In this case, delivery of the sig- nal has no effect on the receiving process. If a signal action is set to SIG_DFL while the signal is pend- ing, the signal remains pending. Ignore signal. Delivery of the signal has no effect on the receiving process. If a signal action is set to SIG_IGN while the signal is pend- ing, the pending signal is discarded. Note that the SIGKILL, SIGSTOP, and SIGCONT signals cannot be ignored. Catch signal. Upon delivery of the signal, the receiving process is to run the signal-catching function specified by the pointer to function. The signal-handler subroutine can be declared as follows: void handler(signal) int signal; The signal parameter is the signal number. A new signal mask is calculated and installed for the duration of the signal-catching function (or until sigprocmask() or sigsuspend() system calls are made). This mask is formed by taking the union of the process signal mask, the mask associated with the action for the signal being delivered, and a mask corresponding to the signal being delivered. The mask associated with the signal-catching function is not allowed to block those signals that cannot be ignored. This is enforced by the kernel without causing an error to be indicated. If and when the sig- nal-catching function returns, the original signal mask is restored (modified by any sigprocmask() calls that were made since the signal- catching function was called) and the receiving process resumes execu- tion at the point it was interrupted. The signal-catching function can cause the process to resume in a dif- ferent context by calling the longjmp() subroutine. When the longjmp() subroutine is called, the process leaves the signal stack, if it is currently on it, and restores the process signal mask to the state when the corresponding setjmp() call was made. Once an action is installed for a specific signal, it remains installed until another action is explicitly requested (by another call to the sigaction() system call), or until one of the exec system calls is called. If a signal action is set to a pointer to a function while the signal is pending, the signal remains pending. When signal-catching functions are invoked asynchronously with process execution, the behavior of some of the functions defined by this stan- dard is unspecified if they are called from a signal-catching function. The following set of functions are reentrant with respect to signals (that is, applications can invoke them, without restriction, from sig- nal-catching functions): tab(@); l l l l. _exit()@access()@alarm()@chdir() chmod()@chown()@close()@creat() dup2()@dup()@exec()@fcntl() fork()@fs- tat()@getegid()@geteuid() getgid()@getgroups()@getpgrp()@getpid() getp- pid()@getuid()@kill()@link() lseek()@mkdir()@mkfifo()@open() pause()@pipe()@read()@rename() rmdir()@setgid()@setpgrp()@setuid() sigaction()@sigaddset()@sigdelset()@sigfillset() siginitset()@sigismem- ber()@signal()@sigpending() sigprocmask()@sigsuspend()@sleep()@statx() tcdrain()@tcflow()@tcflush()@tcgetattr() tcgetprgp()@tcsendbreak()@tc- setattr()@tcsetpgrp() time()@times()@umask()@uname() unlink()@us- tat()@utime()@wait2() wait()@write()@@ All other system calls should not be called from signal-catching func- tions since their behavior is undefined. RELATED INFORMATION Functions: sigaction(2), sigblock(2), sigemptyset(3), siginterrupt(3), siglongjmp(3), sigpause(3), sigpending(2), sigprocmask(2), sigre- turn(2), sigset(3), sigsetjmp(3), sigstack(2), sigsuspend(2), sigvec(2), sigwait(3) delim off signal(4)