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diff --git a/man-pages-posix-2013/man3p/sigaction.3p b/man-pages-posix-2013/man3p/sigaction.3p new file mode 100644 index 0000000..5d68eb2 --- /dev/null +++ b/man-pages-posix-2013/man3p/sigaction.3p @@ -0,0 +1,676 @@ +'\" et +.TH SIGACTION "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual" +.SH PROLOG +This manual page is part of the POSIX Programmer's Manual. +The Linux implementation of this interface may differ (consult +the corresponding Linux manual page for details of Linux behavior), +or the interface may not be implemented on Linux. + +.SH NAME +sigaction +\(em examine and change a signal action +.SH SYNOPSIS +.LP +.nf +#include <signal.h> +.P +int sigaction(int \fIsig\fP, const struct sigaction *restrict \fIact\fP, + struct sigaction *restrict \fIoact\fP); +.fi +.SH DESCRIPTION +The +\fIsigaction\fR() +function allows the calling process to examine and/or specify the +action to be associated with a specific signal. The argument +.IR sig +specifies the signal; acceptable values are defined in +.IR <signal.h> . +.P +The structure +.BR sigaction , +used to describe an action to be taken, is defined in the +.IR <signal.h> +header to include at least the following members: +.ad l +.TS +center box tab(!); +cB | cB | cB +lw(1.5i)B | lw(1.25i)I | lw(2.5i). +Member Type!Member Name!Description +_ +void(*) (int)!sa_handler!T{ +Pointer to a signal-catching function or one of the macros +SIG_IGN or SIG_DFL. +T} +sigset_t!sa_mask!T{ +Additional set of signals to be blocked during execution of +signal-catching function. +T} +int!sa_flags!T{ +Special flags to affect behavior of signal. +T} +T{ +void(*) (int, +.br +\0\0siginfo_t *, void *) +T}!sa_sigaction!Pointer to a signal-catching function. +.TE +.ad b +.P +The storage occupied by +.IR sa_handler +and +.IR sa_sigaction +may overlap, and a conforming application shall not use both +simultaneously. +.P +If the argument +.IR act +is not a null pointer, it points to a structure specifying the action +to be associated with the specified signal. If the argument +.IR oact +is not a null pointer, the action previously associated with the signal +is stored in the location pointed to by the argument +.IR oact . +If the argument +.IR act +is a null pointer, signal handling is unchanged; thus, the call can be +used to enquire about the current handling of a given signal. The +SIGKILL and SIGSTOP signals shall not be added to the signal +mask using this mechanism; this restriction shall be enforced by the +system without causing an error to be indicated. +.P +If the SA_SIGINFO flag (see below) is cleared in the +.IR sa_flags +field of the +.BR sigaction +structure, the +.IR sa_handler +field identifies the action to be associated with the specified signal. +If the SA_SIGINFO flag is set in the +.IR sa_flags +field, the +.IR sa_sigaction +field specifies a signal-catching function. +.P +The +.IR sa_flags +field can be used to modify the behavior of the specified signal. +.P +The following flags, defined in the +.IR <signal.h> +header, can be set in +.IR sa_flags : +.IP SA_NOCLDSTOP 14 +Do not generate SIGCHLD when children stop +or stopped children continue. +.RS 14 +.P +If +.IR sig +is SIGCHLD and the SA_NOCLDSTOP flag is not set in +.IR sa_flags , +and the implementation supports the SIGCHLD signal, then a SIGCHLD +signal shall be generated for the calling process whenever any of its +child processes stop +and a SIGCHLD signal may be generated for the calling +process whenever any of its stopped child processes are continued. +If +.IR sig +is SIGCHLD and the SA_NOCLDSTOP flag is set in +.IR sa_flags , +then the implementation shall not generate a SIGCHLD signal in this +way. +.RE +.IP SA_ONSTACK 14 +If set and an alternate signal stack has been declared with +\fIsigaltstack\fR(), +the signal shall be delivered to the calling process on that stack. +Otherwise, the signal shall be delivered on the current stack. +.IP SA_RESETHAND 14 +If set, the disposition of the signal shall be reset to SIG_DFL and the +SA_SIGINFO flag shall be cleared on entry to the signal handler. +.RS 14 +.TP 10 +.BR Note: +SIGILL and SIGTRAP cannot be automatically reset when delivered; the +system silently enforces this restriction. +.P +Otherwise, the disposition of the signal shall not be modified on entry +to the signal handler. +.P +In addition, if this flag is set, +\fIsigaction\fR() +may behave as if the SA_NODEFER flag were also set. +.RE +.IP SA_RESTART 14 +This flag affects the behavior of interruptible functions; that is, +those specified to fail with +.IR errno +set to +.BR [EINTR] . +If set, and a function specified as interruptible is interrupted by +this signal, the function shall restart and shall not fail with +.BR [EINTR] +unless otherwise specified. If an interruptible function which uses a +timeout is restarted, the duration of the timeout following the restart +is set to an unspecified value that does not exceed the original +timeout value. If the flag is not set, interruptible functions +interrupted by this signal shall fail with +.IR errno +set to +.BR [EINTR] . +.IP SA_SIGINFO 14 +If cleared and the signal is caught, the signal-catching function +shall be entered as: +.RS 14 +.sp +.RS 4 +.nf +\fB +void func(int \fIsigno\fP); +.fi \fR +.P +.RE +.P +where +.IR signo +is the only argument to the signal-catching function. In this case, the +application shall use the +.IR sa_handler +member to describe the signal-catching function and the application +shall not modify the +.IR sa_sigaction +member. +.P +If SA_SIGINFO is set and the signal is caught, the signal-catching +function shall be entered as: +.sp +.RS 4 +.nf +\fB +void func(int \fIsigno\fP, siginfo_t *\fIinfo\fP, void *\fIcontext\fP); +.fi \fR +.P +.RE +.P +where two additional arguments are passed to the signal-catching +function. The second argument shall point to an object of type +.BR siginfo_t +explaining the reason why the signal was generated; the third argument +can be cast to a pointer to an object of type +.BR ucontext_t +to refer to the receiving thread's context that was interrupted when +the signal was delivered. In this case, the application shall use the +.IR sa_sigaction +member to describe the signal-catching function and the application +shall not modify the +.IR sa_handler +member. +.P +The +.IR si_signo +member contains the system-generated signal number. +.P +The +.IR si_errno +member may contain implementation-defined additional error +information; if non-zero, it contains an error number identifying the +condition that caused the signal to be generated. +.P +The +.IR si_code +member contains a code identifying the cause of the signal, as +described in +.IR "Section 2.4.3" ", " "Signal Actions". +.RE +.IP SA_NOCLDWAIT 14 +If set, and +.IR sig +equals SIGCHLD, child processes of the calling processes shall not +be transformed into zombie processes when they terminate. If the calling +process subsequently waits for its children, and the process has no +unwaited-for children that were transformed into zombie processes, it +shall block until all of its children terminate, and +\fIwait\fR(), +\fIwaitid\fR(), +and +\fIwaitpid\fR() +shall fail and set +.IR errno +to +.BR [ECHILD] . +Otherwise, terminating child processes shall be transformed into zombie +processes, unless SIGCHLD is set to SIG_IGN. +.IP SA_NODEFER 14 +If set and +.IR sig +is caught, +.IR sig +shall not be added to the thread's signal mask on entry to the signal +handler unless it is included in +.IR sa_mask . +Otherwise, +.IR sig +shall always be added to the thread's signal mask on entry to the +signal handler. +.P +When a signal is caught by a signal-catching function installed by +\fIsigaction\fR(), +a new signal mask is calculated and installed for the duration of the +signal-catching function (or until a call to either +\fIsigprocmask\fR() +or +\fIsigsuspend\fR() +is made). This mask is formed by taking the union of the current +signal mask and the value of the +.IR sa_mask +for the signal being delivered, and unless SA_NODEFER or +SA_RESETHAND is set, +then including the signal being delivered. If and when the user's +signal handler returns normally, the original signal mask is restored. +.P +Once an action is installed for a specific signal, it shall remain +installed until another action is explicitly requested (by another +call to +\fIsigaction\fR()), +until the SA_RESETHAND flag causes resetting of the handler, +or until one of the +.IR exec +functions is called. +.P +If the previous action for +.IR sig +had been established by +\fIsignal\fR(), +the values of the fields returned in the structure pointed to by +.IR oact +are unspecified, and in particular +.IR oact ->\c +.IR sa_handler +is not necessarily the same value passed to +\fIsignal\fR(). +However, if a pointer to the same structure or a copy thereof is passed +to a subsequent call to +\fIsigaction\fR() +via the +.IR act +argument, handling of the signal shall be as if the original call to +\fIsignal\fR() +were repeated. +.P +If +\fIsigaction\fR() +fails, no new signal handler is installed. +.P +It is unspecified whether an attempt to set the action for a signal +that cannot be caught or ignored to SIG_DFL is ignored or causes an +error to be returned with +.IR errno +set to +.BR [EINVAL] . +.P +If SA_SIGINFO is not set in +.IR sa_flags , +then the disposition of subsequent occurrences of +.IR sig +when it is already pending is implementation-defined; the +signal-catching function shall be invoked with a single argument. +If SA_SIGINFO is set in +.IR sa_flags , +then subsequent occurrences of +.IR sig +generated by +\fIsigqueue\fR() +or as a result of any signal-generating function that supports the +specification of an application-defined value (when +.IR sig +is already pending) shall be queued in FIFO order until delivered or +accepted; the signal-catching function shall be invoked with three +arguments. The application specified value is passed to the +signal-catching function as the +.IR si_value +member of the +.BR siginfo_t +structure. +.P +The result of the use of +\fIsigaction\fR() +and a +\fIsigwait\fR() +function concurrently within a process on the same signal is +unspecified. +.SH "RETURN VALUE" +Upon successful completion, +\fIsigaction\fR() +shall return 0; otherwise, \(mi1 shall be returned, +.IR errno +shall be set to indicate the error, and no new signal-catching function +shall be installed. +.br +.SH ERRORS +The +\fIsigaction\fR() +function shall fail if: +.TP +.BR EINVAL +The +.IR sig +argument is not a valid signal number or an attempt is made to catch a +signal that cannot be caught or ignore a signal that cannot be ignored. +.TP +.BR ENOTSUP +The SA_SIGINFO bit flag is set in the +.IR sa_flags +field of the +.BR sigaction +structure. +.P +The +\fIsigaction\fR() +function may fail if: +.TP +.BR EINVAL +An attempt was made to set the action to SIG_DFL for a signal that +cannot be caught or ignored (or both). +.P +In addition, the +\fIsigaction\fR() +function may fail if the SA_SIGINFO flag is set in the +.IR sa_flags +field of the +.BR sigaction +structure for a signal not in the range SIGRTMIN to SIGRTMAX. +.LP +.IR "The following sections are informative." +.SH EXAMPLES +.SS "Establishing a Signal Handler" +.P +The following example demonstrates the use of +\fIsigaction\fR() +to establish a handler for the SIGINT signal. +.sp +.RS 4 +.nf +\fB +#include <signal.h> +.P +static void handler(int signum) +{ + /* Take appropriate actions for signal delivery */ +} +.P +int main() +{ + struct sigaction sa; +.P + sa.sa_handler = handler; + sigemptyset(&sa.sa_mask); + sa.sa_flags = SA_RESTART; /* Restart functions if + interrupted by handler */ + if (sigaction(SIGINT, &sa, NULL) == \(mi1) + /* Handle error */; +.P + /* Further code */ +} +.fi \fR +.P +.RE +.SH "APPLICATION USAGE" +The +\fIsigaction\fR() +function supersedes the +\fIsignal\fR() +function, and should be used in preference. In particular, +\fIsigaction\fR() +and +\fIsignal\fR() +should not be used in the same process to control the same signal. +The behavior of async-signal-safe functions, as defined in their +respective DESCRIPTION sections, is as specified by this volume of POSIX.1\(hy2008, regardless +of invocation from a signal-catching function. This is the only intended +meaning of the statement that async-signal-safe functions may be used in +signal-catching functions without restrictions. Applications must still +consider all effects of such functions on such things as data structures, +files, and process state. In particular, application developers need +to consider the restrictions on interactions when interrupting +\fIsleep\fR() +and interactions among multiple handles for a file description. The +fact that any specific function is listed as async-signal-safe does not +necessarily mean that invocation of that function from a +signal-catching function is recommended. +.P +In order to prevent errors arising from interrupting non-async-signal-safe +function calls, applications should protect calls to these functions +either by blocking the appropriate signals or through the use of some +programmatic semaphore (see +.IR "\fIsemget\fR\^(\|)", +.IR "\fIsem_init\fR\^(\|)", +.IR "\fIsem_open\fR\^(\|)", +and so on). Note in particular that even the ``safe'' functions may +modify +.IR errno ; +the signal-catching function, if not executing as an independent +thread, should save and restore its value in order to avoid the +possibility that delivery of a signal in between an error return +from a function that sets +.IR errno +and the subsequent examination of +.IR errno +could result in the signal-catching function changing the value of +.IR errno . +Naturally, the same principles apply to the async-signal-safety of +application routines and asynchronous data access. Note that +\fIlongjmp\fR() +and +\fIsiglongjmp\fR() +are not in the list of async-signal-safe functions. This is because +the code executing after +\fIlongjmp\fR() +and +\fIsiglongjmp\fR() +can call any unsafe functions with the same danger as calling those +unsafe functions directly from the signal handler. Applications that +use +\fIlongjmp\fR() +and +\fIsiglongjmp\fR() +from within signal handlers require rigorous protection in order to be +portable. Many of the other functions that are excluded from the list +are traditionally implemented using either +\fImalloc\fR() +or +\fIfree\fR() +functions or the standard I/O library, both of which traditionally +use data structures in a non-async-signal-safe manner. Since any +combination of different functions using a common data structure can +cause async-signal-safety problems, this volume of POSIX.1\(hy2008 does not define the behavior +when any unsafe function is called in a signal handler that interrupts +an unsafe function. +.P +Usually, the signal is executed on the stack that was in effect before +the signal was delivered. An alternate stack may be specified to +receive a subset of the signals being caught. +.P +When the signal handler returns, the receiving thread resumes +execution at the point it was interrupted unless the signal handler +makes other arrangements. If +\fIlongjmp\fR() +or +\fI_longjmp\fR() +is used to leave the signal handler, then the signal mask must be +explicitly restored. +.P +This volume of POSIX.1\(hy2008 defines the third argument of a signal handling function when +SA_SIGINFO is set as a +.BR "void *" +instead of a +.BR "ucontext_t *" , +but without requiring type checking. New applications should +explicitly cast the third argument of the signal handling function to +.BR "ucontext_t *" . +.P +The BSD optional four argument signal handling function is not +supported by this volume of POSIX.1\(hy2008. The BSD declaration would be: +.sp +.RS 4 +.nf +\fB +void handler(int \fIsig\fP, int \fIcode\fP, struct sigcontext *\fIscp\fP, + char *\fIaddr\fP); +.fi \fR +.P +.RE +.P +where +.IR sig +is the signal number, +.IR code +is additional information on certain signals, +.IR scp +is a pointer to the +.BR sigcontext +structure, and +.IR addr +is additional address information. Much the same information is +available in the objects pointed to by the second argument of the +signal handler specified when SA_SIGINFO is set. +.P +Since the +\fIsigaction\fR() +function is allowed but not required to set SA_NODEFER when the +application sets the SA_RESETHAND flag, applications which depend on the +SA_RESETHAND functionality for the newly installed signal handler must +always explicitly set SA_NODEFER when they set SA_RESETHAND in order to +be portable. +.P +See also the rationale for Realtime Signal Generation and Delivery in +the Rationale (Informative) volume of POSIX.1\(hy2008, +.IR "Section B.2.4.2" ", " "Signal Generation and Delivery". +.SH RATIONALE +Although this volume of POSIX.1\(hy2008 requires that signals that cannot be ignored +shall not be added to the signal mask when a signal-catching function +is entered, there is no explicit requirement that subsequent calls to +\fIsigaction\fR() +reflect this in the information returned in the +.IR oact +argument. In other words, if SIGKILL +is included in the +.IR sa_mask +field of +.IR act , +it is unspecified whether or not a subsequent call to +\fIsigaction\fR() +returns with SIGKILL included in the +.IR sa_mask +field of +.IR oact . +.P +The SA_NOCLDSTOP +flag, when supplied in the +.IR act ->\c +.IR sa_flags +parameter, allows overloading SIGCHLD with the System V +semantics that each SIGCLD +signal indicates a single terminated child. Most conforming applications +that catch SIGCHLD are expected to install signal-catching functions +that repeatedly call the +\fIwaitpid\fR() +function with the WNOHANG +flag set, acting on each child for which status is returned, until +\fIwaitpid\fR() +returns zero. If stopped children are not of interest, the use of the +SA_NOCLDSTOP +flag can prevent the overhead from invoking the signal-catching routine +when they stop. +.P +Some historical implementations also define other mechanisms for +stopping processes, such as the +\fIptrace\fR() +function. These implementations usually do not generate a SIGCHLD +signal when processes stop due to this mechanism; however, that is +beyond the scope of this volume of POSIX.1\(hy2008. +.P +This volume of POSIX.1\(hy2008 requires that calls to +\fIsigaction\fR() +that supply a NULL +.IR act +argument succeed, even in the case of signals that cannot be caught or +ignored (that is, SIGKILL +or SIGSTOP). +The System V +\fIsignal\fR() +and BSD +\fIsigvec\fR() +functions return +.BR [EINVAL] +in these cases and, in this respect, their behavior varies from +\fIsigaction\fR(). +.P +This volume of POSIX.1\(hy2008 requires that +\fIsigaction\fR() +properly save and restore a signal action set up by the ISO\ C standard +\fIsignal\fR() +function. However, there is no guarantee that the reverse is true, nor +could there be given the greater amount of information conveyed by the +.BR sigaction +structure. Because of this, applications should avoid using both +functions for the same signal in the same process. Since this cannot +always be avoided in case of general-purpose library routines, they +should always be implemented with +\fIsigaction\fR(). +.P +It was intended that the +\fIsignal\fR() +function should be implementable as a library routine using +\fIsigaction\fR(). +.P +The POSIX Realtime Extension extends the +\fIsigaction\fR() +function as specified by the POSIX.1\(hy1990 standard to allow the application to request +on a per-signal basis via an additional signal action flag that the +extra parameters, including the application-defined signal value, if +any, be passed to the signal-catching function. +.SH "FUTURE DIRECTIONS" +None. +.SH "SEE ALSO" +.IR "Section 2.4" ", " "Signal Concepts", +.IR "\fIexec\fR\^", +.IR "\fIkill\fR\^(\|)", +.IR "\fI_longjmp\fR\^(\|)", +.IR "\fIlongjmp\fR\^(\|)", +.IR "\fIpthread_sigmask\fR\^(\|)", +.IR "\fIraise\fR\^(\|)", +.IR "\fIsemget\fR\^(\|)", +.IR "\fIsem_init\fR\^(\|)", +.IR "\fIsem_open\fR\^(\|)", +.IR "\fIsigaddset\fR\^(\|)", +.IR "\fIsigaltstack\fR\^(\|)", +.IR "\fIsigdelset\fR\^(\|)", +.IR "\fIsigemptyset\fR\^(\|)", +.IR "\fIsigfillset\fR\^(\|)", +.IR "\fIsigismember\fR\^(\|)", +.IR "\fIsignal\fR\^(\|)", +.IR "\fIsigsuspend\fR\^(\|)", +.IR "\fIwait\fR\^(\|)", +.IR "\fIwaitid\fR\^(\|)" +.P +The Base Definitions volume of POSIX.1\(hy2008, +.IR "\fB<signal.h>\fP" +.SH COPYRIGHT +Portions of this text are reprinted and reproduced in electronic form +from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology +-- Portable Operating System Interface (POSIX), The Open Group Base +Specifications Issue 7, Copyright (C) 2013 by the Institute of +Electrical and Electronics Engineers, Inc and The Open Group. +(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the +event of any discrepancy between this version and the original IEEE and +The Open Group Standard, the original IEEE and The Open Group Standard +is the referee document. The original Standard can be obtained online at +http://www.unix.org/online.html . + +Any typographical or formatting errors that appear +in this page are most likely +to have been introduced during the conversion of the source files to +man page format. To report such errors, see +https://www.kernel.org/doc/man-pages/reporting_bugs.html . |