signal(7) | Miscellaneous Information Manual | signal(7) |
signal - overview of signals
V Linuxu jsou podporovány jak POSIX reliable signály (dále jen "standardní signály"), tak POSIX real-time signály.
Každý signál má dispozici, která určuje, jak se proces zachová při jeho přijetí.
Údaje ve sloupci "Akce" níže uvedených tabulek určují výchozí dipozici každého signálu následujícně:
A process can change the disposition of a signal using sigaction(2) or signal(2). (The latter is less portable when establishing a signal handler; see signal(2) for details.) Using these system calls, a process can elect one of the following behaviors to occur on delivery of the signal: perform the default action; ignore the signal; or catch the signal with a signal handler, a programmer-defined function that is automatically invoked when the signal is delivered.
By default, a signal handler is invoked on the normal process stack. It is possible to arrange that the signal handler uses an alternate stack; see sigaltstack(2) for a discussion of how to do this and when it might be useful.
Dispozice signálu je atribut procesu: v mnohovláknových aplikacích je dispozice určitého signálu stejná pro všechna vlákna.
A child created via fork(2) inherits a copy of its parent's signal dispositions. During an execve(2), the dispositions of handled signals are reset to the default; the dispositions of ignored signals are left unchanged.
The following system calls and library functions allow the caller to send a signal:
The following system calls suspend execution of the calling thread until a signal is caught (or an unhandled signal terminates the process):
Rather than asynchronously catching a signal via a signal handler, it is possible to synchronously accept the signal, that is, to block execution until the signal is delivered, at which point the kernel returns information about the signal to the caller. There are two general ways to do this:
A signal may be blocked, which means that it will not be delivered until it is later unblocked. Between the time when it is generated and when it is delivered a signal is said to be pending.
Each thread in a process has an independent signal mask, which indicates the set of signals that the thread is currently blocking. A thread can manipulate its signal mask using pthread_sigmask(3). In a traditional single-threaded application, sigprocmask(2) can be used to manipulate the signal mask.
A child created via fork(2) inherits a copy of its parent's signal mask; the signal mask is preserved across execve(2).
A signal may be process-directed or thread-directed. A process-directed signal is one that is targeted at (and thus pending for) the process as a whole. A signal may be process-directed because it was generated by the kernel for reasons other than a hardware exception, or because it was sent using kill(2) or sigqueue(3). A thread-directed signal is one that is targeted at a specific thread. A signal may be thread-directed because it was generated as a consequence of executing a specific machine-language instruction that triggered a hardware exception (e.g., SIGSEGV for an invalid memory access, or SIGFPE for a math error), or because it was targeted at a specific thread using interfaces such as tgkill(2) or pthread_kill(3).
A process-directed signal may be delivered to any one of the threads that does not currently have the signal blocked. If more than one of the threads has the signal unblocked, then the kernel chooses an arbitrary thread to which to deliver the signal.
A thread can obtain the set of signals that it currently has pending using sigpending(2). This set will consist of the union of the set of pending process-directed signals and the set of signals pending for the calling thread.
A child created via fork(2) initially has an empty pending signal set; the pending signal set is preserved across an execve(2).
Whenever there is a transition from kernel-mode to user-mode execution (e.g., on return from a system call or scheduling of a thread onto the CPU), the kernel checks whether there is a pending unblocked signal for which the process has established a signal handler. If there is such a pending signal, the following steps occur:
Note that if the signal handler does not return (e.g., control is transferred out of the handler using siglongjmp(3), or the handler executes a new program with execve(2)), then the final step is not performed. In particular, in such scenarios it is the programmer's responsibility to restore the state of the signal mask (using sigprocmask(2)), if it is desired to unblock the signals that were blocked on entry to the signal handler. (Note that siglongjmp(3) may or may not restore the signal mask, depending on the savesigs value that was specified in the corresponding call to sigsetjmp(3).)
From the kernel's point of view, execution of the signal handler code is exactly the same as the execution of any other user-space code. That is to say, the kernel does not record any special state information indicating that the thread is currently executing inside a signal handler. All necessary state information is maintained in user-space registers and the user-space stack. The depth to which nested signal handlers may be invoked is thus limited only by the user-space stack (and sensible software design!).
Linux supports the standard signals listed below. The second column of the table indicates which standard (if any) specified the signal: "P1990" indicates that the signal is described in the original POSIX.1-1990 standard; "P2001" indicates that the signal was added in SUSv2 and POSIX.1-2001.
Signál | Standard | Akce | Poznámka |
SIGABRT | P1990 | Core | "Abort" - ukončení funkcí abort(3) |
SIGALRM | P1990 | Term | Signál od časovače, nastaveného funkcí alarm(1) |
SIGBUS | P2001 | Core | "Bus error" - pokus o přístup mimo mapovanou paměť |
SIGCHLD | P1990 | Ign | Zastavení nebo ukončení dětského procesu |
SIGCLD | - | Ign | Synonymum SIGCHLD |
SIGCONT | P1990 | Cont | Pokračování po zastavení |
SIGEMT | - | Term | Emulator trap |
SIGFPE | P1990 | Core | "Floating point exception" - přetečení v pohyblivé řádové čárce |
SIGHUP | P1990 | Term | "Hangup" - při zavěšení na řídícím terminálu |
nebo ukončení řídícího procesu | |||
SIGILL | P1990 | Core | "Illegal Instruction" - neplatná instrukce |
SIGINFO | - | Synonymum SIGPWR | |
SIGINT | P1990 | Term | "Interrupt" - přerušení z klávesnice |
SIGIO | - | Term | Lze pokračovat ve vstupu/výstupu (4.2 BSD) |
SIGIOT | - | Core | IOT - synonymum signálu SIGABRT |
SIGKILL | P1990 | Term | "Kill" - signál pro nepodmíněné ukončení procesu |
SIGLOST | - | Term | Zámek souboru byl ztracen (nepoužívá se) |
SIGPIPE | P1990 | Term | "Broken pipe" - pokus o zápis do roury, |
readers; see pipe(7) | |||
SIGPOLL | P2001 | Term | Pollable event (Sys V); |
Synonymum SIGIO | |||
SIGPROF | P2001 | Term | Časovač používaný při profilování |
SIGPWR | - | Term | Výpadek napájení (Systém V) |
SIGQUIT | P1990 | Core | "Quit" - ukončení z klávesnice |
SIGSEGV | P1990 | Core | Odkaz na nepřípustnou adresu v paměti |
SIGSTKFLT | - | Term | Chyba zásobníku koprocesoru (nepoužívá se) |
SIGSTOP | P1990 | Stop | Zastavení procesu |
SIGTSTP | P1990 | Stop | Stop typed at terminal |
SIGSYS | P2001 | Core | Bad system call (SVr4); |
see also seccomp(2) | |||
SIGTERM | P1990 | Term | "Termination" - signál ukončení |
SIGTRAP | P2001 | Core | Přerušení při ladění (trasování,breakpoint) |
SIGTTIN | P1990 | Stop | Terminal input for background process |
SIGTTOU | P1990 | Stop | Terminal output for background process |
SIGUNUSED | - | Core | Synonymous with SIGSYS |
SIGURG | P2001 | Ign | Soket přijal data s příznakem Urgent (4.2 BSD) |
SIGUSR1 | P1990 | Term | Signál 1 definovaný uživatelem |
SIGUSR2 | P1990 | Term | Signál 2 definovaný uživatelem |
SIGVTALRM | P2001 | Term | Virtuální časovač (4.2 BSD) |
SIGXCPU | P2001 | Core | Překročen limit času CPU (4.2 BSD); |
viz setrlimit(2) | |||
SIGXFSZ | P2001 | Core | Překročen limit velikosti souboru (4.2 BSD); |
viz setrlimit(2) | |||
SIGWINCH | - | Ign | Změna velikosti okna (4.3 BSD, Sun) |
Signály SIGKILL a SIGSTOP nemohou být zachyceny, blokovány ani ignorovány.
Až po Linux 2.2 včetně bylo výchozí chování pro SIGSYS, SIGXCPU, SIGXFSZ, a (na architekturách jiných než SPARC a MIPS) SIGBUS ukončit proces (bez core dump). (Na některých jiných UNIXových systémech bylo výchozí akcí pro SIGXCPU a SIGXFSZ ukončení procesu bez core dump.) Linux 2.4 splňuje požadavky POSIX.1-2001 pro tyto signály, ukončuje procesy s core dump.
SIGEMT není specifikován v POSIX.1-2001, ale stejně je přítomen na většině ostatních UNIXových systémů, kde je výchozí akcí obvykle ukončení procesu s core dump.
SIGPWR (není specifikován v POSIX.1-2001) na většině ostatních UNIXových systémů, kde se objevuje, je obvykle ignorován.
SIGIO (není specifikován v POSIX.1-2001) na některých dalších UNIXech je jako výchozí ignorován.
If multiple standard signals are pending for a process, the order in which the signals are delivered is unspecified.
Standard signals do not queue. If multiple instances of a standard signal are generated while that signal is blocked, then only one instance of the signal is marked as pending (and the signal will be delivered just once when it is unblocked). In the case where a standard signal is already pending, the siginfo_t structure (see sigaction(2)) associated with that signal is not overwritten on arrival of subsequent instances of the same signal. Thus, the process will receive the information associated with the first instance of the signal.
The numeric value for each signal is given in the table below. As shown in the table, many signals have different numeric values on different architectures. The first numeric value in each table row shows the signal number on x86, ARM, and most other architectures; the second value is for Alpha and SPARC; the third is for MIPS; and the last is for PARISC. A dash (-) denotes that a signal is absent on the corresponding architecture.
Signál | x86/ARM | Alpha/ | MIPS | PARISC | Poznámky |
most others | SPARC | ||||
SIGHUP | 1 | 1 | 1 | 1 | |
SIGINT | 2 | 2 | 2 | 2 | |
SIGQUIT | 3 | 3 | 3 | 3 | |
SIGILL | 4 | 4 | 4 | 4 | |
SIGTRAP | 5 | 5 | 5 | 5 | |
SIGABRT | 6 | 6 | 6 | 6 | |
SIGIOT | 6 | 6 | 6 | 6 | |
SIGBUS | 7 | 10 | 10 | 10 | |
SIGEMT | - | 7 | 7 | - | |
SIGFPE | 8 | 8 | 8 | 8 | |
SIGKILL | 9 | 9 | 9 | 9 | |
SIGUSR1 | 10 | 30 | 16 | 16 | |
SIGSEGV | 11 | 11 | 11 | 11 | |
SIGUSR2 | 12 | 31 | 17 | 17 | |
SIGPIPE | 13 | 13 | 13 | 13 | |
SIGALRM | 14 | 14 | 14 | 14 | |
SIGTERM | 15 | 15 | 15 | 15 | |
SIGSTKFLT | 16 | - | - | 7 | |
SIGCHLD | 17 | 20 | 18 | 18 | |
SIGCLD | - | - | 18 | - | |
SIGCONT | 18 | 19 | 25 | 26 | |
SIGSTOP | 19 | 17 | 23 | 24 | |
SIGTSTP | 20 | 18 | 24 | 25 | |
SIGTTIN | 21 | 21 | 26 | 27 | |
SIGTTOU | 22 | 22 | 27 | 28 | |
SIGURG | 23 | 16 | 21 | 29 | |
SIGXCPU | 24 | 24 | 30 | 12 | |
SIGXFSZ | 25 | 25 | 31 | 30 | |
SIGVTALRM | 26 | 26 | 28 | 20 | |
SIGPROF | 27 | 27 | 29 | 21 | |
SIGWINCH | 28 | 28 | 20 | 23 | |
SIGIO | 29 | 23 | 22 | 22 | |
SIGPOLL | Same as SIGIO | ||||
SIGPWR | 30 | 29/- | 19 | 19 | |
SIGINFO | - | 29/- | - | - | |
SIGLOST | - | -/29 | - | - | |
SIGSYS | 31 | 12 | 12 | 31 | |
SIGUNUSED | 31 | - | - | 31 |
Note the following:
Starting with Linux 2.2, Linux supports real-time signals as originally defined in the POSIX.1b real-time extensions (and now included in POSIX.1-2001). The range of supported real-time signals is defined by the macros SIGRTMIN and SIGRTMAX. POSIX.1-2001 requires that an implementation support at least _POSIX_RTSIG_MAX (8) real-time signals.
Linux podporuje 33 různých real-time signálů očíslovaných 32 až 64. Nicméně implementace POSIX threads v glibc používá interně dva (pro NPTL) nebo tři (pro LinuxThreads) real-time signály (viz pthreads(7)), a podle toho upravuje hodnotu SIGRTMIN (na 34 nebo 35). protože rozsah dostupných real-time signálů se liší v závislosti na implementaci vláken v glibc (může se měnit za běhu v závislosti na jádře a glibc) a navíc rozsah real-time signálů se mezi UNIXovými systémy liší, programy by nikdy neměly odkazovat na real-time signály pevně danými čísly, místo toho by měly používat notaci SIGRTMIN+n, a za běhu kontrolovat, zda SIGRTMIN+n nepřesahuje SIGRTMAX.
Na rozdíl od standardních signálů nemají real-time signály stanovený význam: Celá sada real-time signálů může být použita pro účely definované aplikací.
Výchozí akcí pro nezpracovaný real-time signál je ukončení procesu, který jej přijal.
Real-time signály se liší následujícně:
Pokud má proces nevyřízené zároveň real-time a standardní signály, POSIX neurčuje, které mají být doručeny jako první. Linux, stejně jako mnoho jiných implementací, v takovém případě upřednostňí standardní signály.
According to POSIX, an implementation should permit at least _POSIX_SIGQUEUE_MAX (32) real-time signals to be queued to a process. However, Linux does things differently. Up to and including Linux 2.6.7, Linux imposes a system-wide limit on the number of queued real-time signals for all processes. This limit can be viewed and (with privilege) changed via the /proc/sys/kernel/rtsig-max file. A related file, /proc/sys/kernel/rtsig-nr, can be used to find out how many real-time signals are currently queued. In Linux 2.6.8, these /proc interfaces were replaced by the RLIMIT_SIGPENDING resource limit, which specifies a per-user limit for queued signals; see setrlimit(2) for further details.
The addition of real-time signals required the widening of the signal set structure (sigset_t) from 32 to 64 bits. Consequently, various system calls were superseded by new system calls that supported the larger signal sets. The old and new system calls are as follows:
Jádro 2.0 a dřívější | Linux 2.2 and later |
sigaction(2) | rt_sigaction(2) |
sigpending(2) | rt_sigpending(2) |
sigprocmask(2) | rt_sigprocmask(2) |
sigreturn(2) | rt_sigreturn(2) |
sigsuspend(2) | rt_sigsuspend(2) |
sigtimedwait(2) | rt_sigtimedwait(2) |
Pokud je signal handler vyvolán v okamžiku, kdy je systémové volání nebo funkce knihovny blokována, pak:
Která z těchto možností nastane, záleží na rozhraní a na tom, zda byl signal handler definován s pomocí vlajky SA_RESTART (viz sigaction(2)). Podrobnosti se mezi UNIXovými systémy liší; dále jsou uvedeny pro Linux.
If a blocked call to one of the following interfaces is interrupted by a signal handler, then the call is automatically restarted after the signal handler returns if the SA_RESTART flag was used; otherwise the call fails with the error EINTR:
The following interfaces are never restarted after being interrupted by a signal handler, regardless of the use of SA_RESTART; they always fail with the error EINTR when interrupted by a signal handler:
Funkce sleep(3) se také při přerušení signal handlerem nerestartuje, nýbrž vrátí úspěch: počet sekund, které zbývají ke spaní.
In certain circumstances, the seccomp(2) user-space notification feature can lead to restarting of system calls that would otherwise never be restarted by SA_RESTART; for details, see seccomp_unotify(2).
V Linuxu mohou některá blokující rozhraní selhat s chybou EINTR i bez signal handlerů, pokud je proces zastaven jedním ze stop signálů a poté obnoven pomocí SIGCONT. Toto chování neodporuje POSIX.1 a neobjevuje se v jiných systémech.
Linuxová rozhraní, v nichž se toto chování projevuje, jsou:
POSIX.1, s uvedenými výjimkami.
For a discussion of async-signal-safe functions, see signal-safety(7).
The /proc/[pid]/task/[tid]/status file contains various fields that show the signals that a thread is blocking (SigBlk), catching (SigCgt), or ignoring (SigIgn). (The set of signals that are caught or ignored will be the same across all threads in a process.) Other fields show the set of pending signals that are directed to the thread (SigPnd) as well as the set of pending signals that are directed to the process as a whole (ShdPnd). The corresponding fields in /proc/[pid]/status show the information for the main thread. See proc(5) for further details.
There are six signals that can be delivered as a consequence of a hardware exception: SIGBUS, SIGEMT, SIGFPE, SIGILL, SIGSEGV, and SIGTRAP. Which of these signals is delivered, for any given hardware exception, is not documented and does not always make sense.
For example, an invalid memory access that causes delivery of SIGSEGV on one CPU architecture may cause delivery of SIGBUS on another architecture, or vice versa.
For another example, using the x86 int instruction with a forbidden argument (any number other than 3 or 128) causes delivery of SIGSEGV, even though SIGILL would make more sense, because of how the CPU reports the forbidden operation to the kernel.
kill(1), clone(2), getrlimit(2), kill(2), pidfd_send_signal(2), restart_syscall(2), rt_sigqueueinfo(2), setitimer(2), setrlimit(2), sgetmask(2), sigaction(2), sigaltstack(2), signal(2), signalfd(2), sigpending(2), sigprocmask(2), sigreturn(2), sigsuspend(2), sigwaitinfo(2), abort(3), bsd_signal(3), killpg(3), longjmp(3), pthread_sigqueue(3), raise(3), sigqueue(3), sigset(3), sigsetops(3), sigvec(3), sigwait(3), strsignal(3), swapcontext(3), sysv_signal(3), core(5), proc(5), nptl(7), pthreads(7), sigevent(7)
Překlad této příručky do španělštiny vytvořili Marek Kubita <Kubitovi@mbox.lantanet.cz> a Pavel Heimlich <tropikhajma@gmail.com>
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Pokud narazíte na nějaké chyby v překladu této příručky, pošlete e-mail na adresu translation-team-cs@lists.sourceforge.net.
5. února 2023 | Linux man-pages 6.03 |