man7/signal.7

   1 '\" t
   2 .\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
   3 .\" and Copyright (c) 2002, 2006 by Michael Kerrisk <mtk.manpages@gmail.com>
   4 .\" and Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
   5 .\"     <mtk.manpages@gmail.com>
   6 .\"
   7 .\" Permission is granted to make and distribute verbatim copies of this
   8 .\" manual provided the copyright notice and this permission notice are
   9 .\" preserved on all copies.
  10 .\"
  11 .\" Permission is granted to copy and distribute modified versions of this
  12 .\" manual under the conditions for verbatim copying, provided that the
  13 .\" entire resulting derived work is distributed under the terms of a
  14 .\" permission notice identical to this one.
  15 .\"
  16 .\" Since the Linux kernel and libraries are constantly changing, this
  17 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  18 .\" responsibility for errors or omissions, or for damages resulting from
  19 .\" the use of the information contained herein.  The author(s) may not
  20 .\" have taken the same level of care in the production of this manual,
  21 .\" which is licensed free of charge, as they might when working
  22 .\" professionally.
  23 .\"
  24 .\" Formatted or processed versions of this manual, if unaccompanied by
  25 .\" the source, must acknowledge the copyright and authors of this work.
  26 .\"
  27 .\" Modified Sat Jul 24 17:34:08 1993 by Rik Faith (faith@cs.unc.edu)
  28 .\" Modified Sun Jan  7 01:41:27 1996 by Andries Brouwer (aeb@cwi.nl)
  29 .\" Modified Sun Apr 14 12:02:29 1996 by Andries Brouwer (aeb@cwi.nl)
  30 .\" Modified Sat Nov 13 16:28:23 1999 by Andries Brouwer (aeb@cwi.nl)
  31 .\" Modified 10 Apr 2002, by Michael Kerrisk <mtk.manpages@gmail.com>
  32 .\" Modified  7 Jun 2002, by Michael Kerrisk <mtk.manpages@gmail.com>
  33 .\"     Added information on real-time signals
  34 .\" Modified 13 Jun 2002, by Michael Kerrisk <mtk.manpages@gmail.com>
  35 .\"     Noted that SIGSTKFLT is in fact unused
  36 .\" 2004-12-03, Modified mtk, added notes on RLIMIT_SIGPENDING
  37 .\" 2006-04-24, mtk, Added text on changing signal dispositions,
  38 .\"             signal mask, and pending signals.
  39 .\" 2008-07-04, mtk:
  40 .\"     Added section on system call restarting (SA_RESTART)
  41 .\"     Added section on stop/cont signals interrupting syscalls.
  42 .\"
  43 .TH SIGNAL 7  2008-10-05 "Linux" "Linux Programmer's Manual"
  44 .SH NAME
  45 signal \- list of available signals
  46 .SH DESCRIPTION
  47 Linux supports both POSIX reliable signals (hereinafter
  48 "standard signals") and POSIX real-time signals.
  49 .SS "Signal Dispositions"
  50 Each signal has a current
  51 .IR disposition ,
  52 which determines how the process behaves when it is delivered
  53 the signal.
  54
  55 The entries in the "Action" column of the tables below specify
  56 the default disposition for each signal, as follows:
  57 .IP Term
  58 Default action is to terminate the process.
  59 .IP Ign
  60 Default action is to ignore the signal.
  61 .IP Core
  62 Default action is to terminate the process and dump core (see
  63 .BR core (5)).
  64 .IP Stop
  65 Default action is to stop the process.
  66 .IP Cont
  67 Default action is to continue the process if it is currently stopped.
  68 .PP
  69 A process can change the disposition of a signal using
  70 .BR sigaction (2)
  71 or (less portably)
  72 .BR signal (2).
  73 Using these system calls, a process can elect one of the
  74 following behaviors to occur on delivery of the signal:
  75 perform the default action; ignore the signal;
  76 or catch the signal with a
  77 .IR "signal handler" ,
  78 a programmer-defined function that is automatically invoked
  79 when the signal is delivered.
  80
  81 The signal disposition is a per-process attribute:
  82 in a multithreaded application, the disposition of a
  83 particular signal is the same for all threads.
  84
  85 A child created via
  86 .BR fork (2)
  87 inherits a copy of its parent's signal dispositions.
  88 During an
  89 .BR execve (2),
  90 the dispositions of handled signals are reset to the default;
  91 the dispositions of ignored signals are left unchanged.
  92 .SS Sending a Signal
  93 The following system calls and library functions allow
  94 the caller to send a signal:
  95 .TP 12
  96 .BR raise (3)
  97 Sends a signal to the calling thread.
  98 .TP
  99 .BR kill (2)
 100 Sends a signal to a specified process,
 101 to all members of a specified process group,
 102 or to all processes on the system.
 103 .TP
 104 .BR killpg (2)
 105 Sends a signal to all of the members of a specified process group.
 106 .TP
 107 .BR pthread_kill (3)
 108 Sends a signal to a specified POSIX thread in the same process as
 109 the caller.
 110 .TP
 111 .BR tgkill (2)
 112 Sends a signal to a specified thread within a specific process.
 113 (This is the system call used to implement
 114 .BR pthread_kill (3).)
 115 .TP
 116 .BR sigqueue (2)
 117 Sends a real-time signal with accompanying data to a specified process.
 118 .SS "Signal Mask and Pending Signals"
 119 A signal may be
 120 .IR blocked ,
 121 which means that it will not be delivered until it is later unblocked.
 122 Between the time when it is generated and when it is delivered
 123 a signal is said to be
 124 .IR pending .
 125
 126 Each thread in a process has an independent
 127 .IR "signal mask" ,
 128 which indicates the set of signals that the thread is currently blocking.
 129 A thread can manipulate its signal mask using
 130 .BR pthread_sigmask (3).
 131 In a traditional single-threaded application,
 132 .BR sigprocmask (2)
 133 can be used to manipulate the signal mask.
 134
 135 A child created via
 136 .BR fork (2)
 137 inherits a copy of its parent's signal mask;
 138 the signal mask is preserved across
 139 .BR execve (2).
 140
 141 A signal may be generated (and thus pending)
 142 for a process as a whole (e.g., when sent using
 143 .BR kill (2))
 144 or for a specific thread (e.g., certain signals,
 145 such as
 146 .B SIGSEGV
 147 and
 148 .BR SIGFPE ,
 149 generated as a
 150 consequence of executing a specific machine-language instruction
 151 are thread directed, as are signals targeted at a specific thread using
 152 .BR pthread_kill (3)).
 153 A process-directed signal may be delivered to any one of the
 154 threads that does not currently have the signal blocked.
 155 If more than one of the threads has the signal unblocked, then the
 156 kernel chooses an arbitrary thread to which to deliver the signal.
 157
 158 A thread can obtain the set of signals that it currently has pending
 159 using
 160 .BR sigpending (2).
 161 This set will consist of the union of the set of pending
 162 process-directed signals and the set of signals pending for
 163 the calling thread.
 164
 165 A child created via
 166 .BR fork (2)
 167 initially has an empty pending signal set;
 168 the pending signal set is preserved across an
 169 .BR execve (2).
 170 .SS "Standard Signals"
 171 Linux supports the standard signals listed below.
 172 Several signal numbers
 173 are architecture-dependent, as indicated in the "Value" column.
 174 (Where three values are given, the first one is usually valid for
 175 alpha and sparc,
 176 the middle one for ix86, ia64, ppc, s390, arm and sh,
 177 and the last one for mips.
 178 .\" parisc is a law unto itself
 179 A \- denotes that a signal is absent on the corresponding architecture.)
 180
 181 First the signals described in the original POSIX.1-1990 standard.
 182 .TS
 183 l c c l
 184 ____
 185 lB c c l.
 186 Signal  Value   Action  Comment
 187 SIGHUP  \01     Term    Hangup detected on controlling terminal
 188                         or death of controlling process
 189 SIGINT  \02     Term    Interrupt from keyboard
 190 SIGQUIT \03     Core    Quit from keyboard
 191 SIGILL  \04     Core    Illegal Instruction
 192 SIGABRT \06     Core    Abort signal from \fBabort\fP(3)
 193 SIGFPE  \08     Core    Floating point exception
 194 SIGKILL \09     Term    Kill signal
 195 SIGSEGV 11      Core    Invalid memory reference
 196 SIGPIPE 13      Term    Broken pipe: write to pipe with no
 197                         readers
 198 SIGALRM 14      Term    Timer signal from \fBalarm\fP(2)
 199 SIGTERM 15      Term    Termination signal
 200 SIGUSR1 30,10,16        Term    User-defined signal 1
 201 SIGUSR2 31,12,17        Term    User-defined signal 2
 202 SIGCHLD 20,17,18        Ign     Child stopped or terminated
 203 SIGCONT 19,18,25        Cont    Continue if stopped
 204 SIGSTOP 17,19,23        Stop    Stop process
 205 SIGTSTP 18,20,24        Stop    Stop typed at tty
 206 SIGTTIN 21,21,26        Stop    tty input for background process
 207 SIGTTOU 22,22,27        Stop    tty output for background process
 208 .TE
 209
 210 The signals
 211 .B SIGKILL
 212 and
 213 .B SIGSTOP
 214 cannot be caught, blocked, or ignored.
 215
 216 Next the signals not in the POSIX.1-1990 standard but described in
 217 SUSv2 and POSIX.1-2001.
 218 .TS
 219 l c c l
 220 ____
 221 lB c c l.
 222 Signal  Value   Action  Comment
 223 SIGBUS  10,7,10 Core    Bus error (bad memory access)
 224 SIGPOLL         Term    Pollable event (Sys V).
 225                         Synonym for \fBSIGIO\fP
 226 SIGPROF 27,27,29        Term    Profiling timer expired
 227 SIGSYS  12,\-,12        Core    Bad argument to routine (SVr4)
 228 SIGTRAP 5       Core    Trace/breakpoint trap
 229 SIGURG  16,23,21        Ign     Urgent condition on socket (4.2BSD)
 230 SIGVTALRM       26,26,28        Term    Virtual alarm clock (4.2BSD)
 231 SIGXCPU 24,24,30        Core    CPU time limit exceeded (4.2BSD)
 232 SIGXFSZ 25,25,31        Core    File size limit exceeded (4.2BSD)
 233 .TE
 234
 235 Up to and including Linux 2.2, the default behavior for
 236 .BR SIGSYS ", " SIGXCPU ", " SIGXFSZ ", "
 237 and (on architectures other than SPARC and MIPS)
 238 .B SIGBUS
 239 was to terminate the process (without a core dump).
 240 (On some other Unix systems the default action for
 241 .BR SIGXCPU " and " SIGXFSZ
 242 is to terminate the process without a core dump.)
 243 Linux 2.4 conforms to the POSIX.1-2001 requirements for these signals,
 244 terminating the process with a core dump.
 245
 246 Next various other signals.
 247 .TS
 248 l c c l
 249 ____
 250 lB c c l.
 251 Signal  Value   Action  Comment
 252 SIGIOT  6       Core    IOT trap. A synonym for \fBSIGABRT\fP
 253 SIGEMT  7,\-,7  Term
 254 SIGSTKFLT       \-,16,\-        Term    Stack fault on coprocessor (unused)
 255 SIGIO   23,29,22        Term    I/O now possible (4.2BSD)
 256 SIGCLD  \-,\-,18        Ign     A synonym for \fBSIGCHLD\fP
 257 SIGPWR  29,30,19        Term    Power failure (System V)
 258 SIGINFO 29,\-,\-                A synonym for \fBSIGPWR\fP
 259 SIGLOST \-,\-,\-        Term    File lock lost
 260 SIGWINCH        28,28,20        Ign     Window resize signal (4.3BSD, Sun)
 261 SIGUNUSED       \-,31,\-        Term    Unused signal (will be \fBSIGSYS\fP)
 262 .TE
 263
 264 (Signal 29 is
 265 .B SIGINFO
 266 /
 267 .B SIGPWR
 268 on an alpha but
 269 .B SIGLOST
 270 on a sparc.)
 271
 272 .B SIGEMT
 273 is not specified in POSIX.1-2001, but nevertheless appears
 274 on most other Unix systems,
 275 where its default action is typically to terminate
 276 the process with a core dump.
 277
 278 .B SIGPWR
 279 (which is not specified in POSIX.1-2001) is typically ignored
 280 by default on those other Unix systems where it appears.
 281
 282 .B SIGIO
 283 (which is not specified in POSIX.1-2001) is ignored by default
 284 on several other Unix systems.
 285 .SS "Real-time Signals"
 286 Linux supports real-time signals as originally defined in the POSIX.1b
 287 real-time extensions (and now included in POSIX.1-2001).
 288 The range of supported real-time signals is defined by the macros
 289 .B SIGRTMIN
 290 and
 291 .BR SIGRTMAX .
 292 POSIX.1-2001 requires that an implementation support at least
 293 .B _POSIX_RTSIG_MAX
 294 (8) real-time signals.
 295 .PP
 296 The Linux kernel supports a range of 32 different real-time
 297 signals, numbered 33 to 64.
 298 However, the glibc POSIX threads implementation internally uses
 299 two (for NPTL) or three (for LinuxThreads) real-time signals
 300 (see
 301 .BR pthreads (7)),
 302 and adjusts the value of
 303 .B SIGRTMIN
 304 suitably (to 34 or 35).
 305 Because the range of available real-time signals varies according
 306 to the glibc threading implementation (and this variation can occur
 307 at run time according to the available kernel and glibc),
 308 and indeed the range of real-time signals varies across Unix systems,
 309 programs should
 310 .IR "never refer to real-time signals using hard-coded numbers" ,
 311 but instead should always refer to real-time signals using the notation
 312 .BR SIGRTMIN +n,
 313 and include suitable (run-time) checks that
 314 .BR SIGRTMIN +n
 315 does not exceed
 316 .BR SIGRTMAX .
 317 .PP
 318 Unlike standard signals, real-time signals have no predefined meanings:
 319 the entire set of real-time signals can be used for application-defined
 320 purposes.
 321 (Note, however, that the LinuxThreads implementation uses the first
 322 three real-time signals.)
 323 .PP
 324 The default action for an unhandled real-time signal is to terminate the
 325 receiving process.
 326 .PP
 327 Real-time signals are distinguished by the following:
 328 .IP 1. 4
 329 Multiple instances of real-time signals can be queued.
 330 By contrast, if multiple instances of a standard signal are delivered
 331 while that signal is currently blocked, then only one instance is queued.
 332 .IP 2. 4
 333 If the signal is sent using
 334 .BR sigqueue (2),
 335 an accompanying value (either an integer or a pointer) can be sent
 336 with the signal.
 337 If the receiving process establishes a handler for this signal using the
 338 .B SA_SIGINFO
 339 flag to
 340 .BR sigaction (2)
 341 then it can obtain this data via the
 342 .I si_value
 343 field of the
 344 .I siginfo_t
 345 structure passed as the second argument to the handler.
 346 Furthermore, the
 347 .I si_pid
 348 and
 349 .I si_uid
 350 fields of this structure can be used to obtain the PID
 351 and real user ID of the process sending the signal.
 352 .IP 3. 4
 353 Real-time signals are delivered in a guaranteed order.
 354 Multiple real-time signals of the same type are delivered in the order
 355 they were sent.
 356 If different real-time signals are sent to a process, they are delivered
 357 starting with the lowest-numbered signal.
 358 (I.e., low-numbered signals have highest priority.)
 359 By contrast, if multiple standard signals are pending for a process,
 360 the order in which they are delivered is unspecified.
 361 .PP
 362 If both standard and real-time signals are pending for a process,
 363 POSIX leaves it unspecified which is delivered first.
 364 Linux, like many other implementations, gives priority
 365 to standard signals in this case.
 366 .PP
 367 According to POSIX, an implementation should permit at least
 368 .B _POSIX_SIGQUEUE_MAX
 369 (32) real-time signals to be queued to
 370 a process.
 371 However, Linux does things differently.
 372 In kernels up to and including 2.6.7, Linux imposes
 373 a system-wide limit on the number of queued real-time signals
 374 for all processes.
 375 This limit can be viewed and (with privilege) changed via the
 376 .I /proc/sys/kernel/rtsig-max
 377 file.
 378 A related file,
 379 .IR /proc/sys/kernel/rtsig-nr ,
 380 can be used to find out how many real-time signals are currently queued.
 381 In Linux 2.6.8, these
 382 .I /proc
 383 interfaces were replaced by the
 384 .B RLIMIT_SIGPENDING
 385 resource limit, which specifies a per-user limit for queued
 386 signals; see
 387 .BR setrlimit (2)
 388 for further details.
 389 .SS "Async-signal-safe functions"
 390 .PP
 391 A signal handling routine established by
 392 .BR sigaction (2)
 393 or
 394 .BR signal (2)
 395 must be very careful, since processing elsewhere may be interrupted
 396 at some arbitrary point in the execution of the program.
 397 POSIX has the concept of "safe function".
 398 If a signal interrupts the execution of an unsafe function, and
 399 .I handler
 400 calls an unsafe function, then the behavior of the program is undefined.
 401
 402 POSIX.1-2004 (also known as POSIX.1-2001 Technical Corrigendum 2)
 403 requires an implementation to guarantee that the following
 404 functions can be safely called inside a signal handler:
 405
 406 .in +4
 407 .nf
 408 _Exit()
 409 _exit()
 410 abort()
 411 accept()
 412 access()
 413 aio_error()
 414 aio_return()
 415 aio_suspend()
 416 alarm()
 417 bind()
 418 cfgetispeed()
 419 cfgetospeed()
 420 cfsetispeed()
 421 cfsetospeed()
 422 chdir()
 423 chmod()
 424 chown()
 425 clock_gettime()
 426 close()
 427 connect()
 428 creat()
 429 dup()
 430 dup2()
 431 execle()
 432 execve()
 433 fchmod()
 434 fchown()
 435 fcntl()
 436 fdatasync()
 437 fork()
 438 fpathconf()
 439 fstat()
 440 fsync()
 441 ftruncate()
 442 getegid()
 443 geteuid()
 444 getgid()
 445 getgroups()
 446 getpeername()
 447 getpgrp()
 448 getpid()
 449 getppid()
 450 getsockname()
 451 getsockopt()
 452 getuid()
 453 kill()
 454 link()
 455 listen()
 456 lseek()
 457 lstat()
 458 mkdir()
 459 mkfifo()
 460 open()
 461 pathconf()
 462 pause()
 463 pipe()
 464 poll()
 465 posix_trace_event()
 466 pselect()
 467 raise()
 468 read()
 469 readlink()
 470 recv()
 471 recvfrom()
 472 recvmsg()
 473 rename()
 474 rmdir()
 475 select()
 476 sem_post()
 477 send()
 478 sendmsg()
 479 sendto()
 480 setgid()
 481 setpgid()
 482 setsid()
 483 setsockopt()
 484 setuid()
 485 shutdown()
 486 sigaction()
 487 sigaddset()
 488 sigdelset()
 489 sigemptyset()
 490 sigfillset()
 491 sigismember()
 492 signal()
 493 sigpause()
 494 sigpending()
 495 sigprocmask()
 496 sigqueue()
 497 sigset()
 498 sigsuspend()
 499 sleep()
 500 sockatmark()
 501 socket()
 502 socketpair()
 503 stat()
 504 symlink()
 505 sysconf()
 506 tcdrain()
 507 tcflow()
 508 tcflush()
 509 tcgetattr()
 510 tcgetpgrp()
 511 tcsendbreak()
 512 tcsetattr()
 513 tcsetpgrp()
 514 time()
 515 timer_getoverrun()
 516 timer_gettime()
 517 timer_settime()
 518 times()
 519 umask()
 520 uname()
 521 unlink()
 522 utime()
 523 wait()
 524 waitpid()
 525 write()
 526 .fi
 527 .in
 528 .PP
 529 POSIX.1-2008 removes fpathconf(), pathconf(), and sysconf()
 530 from the above list, and adds the following functions:
 531 .PP
 532 .in +4n
 533 .nf
 534 execl()
 535 execv()
 536 faccessat()
 537 fchmodat()
 538 fchownat()
 539 fexecve()
 540 fstatat()
 541 futimens()
 542 linkat()
 543 mkdirat()
 544 mkfifoat()
 545 mknod()
 546 mknodat()
 547 openat()
 548 readlinkat()
 549 renameat()
 550 symlinkat()
 551 unlinkat()
 552 utimensat()
 553 utimes()
 554 .fi
 555 .in
 556 .SS Interruption of System Calls and Library Functions by Signal Handlers
 557 If a signal handler is invoked while a system call or library
 558 function call is blocked, then either:
 559 .IP * 2
 560 the call is automatically restarted after the signal handler returns; or
 561 .IP *
 562 the call fails with the error
 563 .BR EINTR .
 564 .PP
 565 Which of these two behaviors occurs depends on the interface and
 566 whether or not the signal handler was established using the
 567 .BR SA_RESTART
 568 flag (see
 569 .BR sigaction (2)).
 570 The details vary across Unix systems;
 571 below, the details for Linux.
 572
 573 If a blocked call to one of the following interfaces is interrupted
 574 by a signal handler, then the call will be automatically restarted
 575 after the signal handler returns if the
 576 .BR SA_RESTART
 577 flag was used; otherwise the call will fail with the error
 578 .BR EINTR :
 579 .\" The following system calls use ERESTARTSYS,
 580 .\" so that they are restartable
 581 .RS 4
 582 .IP * 2
 583 .BR read (2),
 584 .BR readv (2),
 585 .BR write (2),
 586 .BR writev (2),
 587 and
 588 .BR ioctl (2)
 589 calls on "slow" devices.
 590 A "slow" device is one where the I/O call may block for an
 591 indefinite time, for example, a terminal, pipe, or socket.
 592 (A disk is not a slow device according to this definition.)
 593 If an I/O call on a slow device has already transferred some
 594 data by the time it is interrupted by a signal handler,
 595 then the call will return a success status
 596 (normally, the number of bytes transferred).
 597 .IP *
 598 .BR open (2),
 599 if it can block (e.g., when opening a FIFO; see
 600 .BR fifo (7)).
 601 .IP *
 602 .BR wait (2),
 603 .BR wait3 (2),
 604 .BR wait4 (2),
 605 .BR waitid (2),
 606 and
 607 .BR waitpid (2).
 608 .IP *
 609 Socket interfaces:
 610 .\" If a timeout (setsockopt()) is in effect on the socket, then these
 611 .\" system calls switch to using EINTR.  Consequently, they and are not
 612 .\" automatically restarted, and they show the stop/cont behavior
 613 .\" described below.  (Verified from 2.6.26 source, and by experiment; mtk)
 614 .BR accept (2),
 615 .BR connect (2),
 616 .BR recv (2),
 617 .BR recvfrom (2),
 618 .BR recvmsg (2),
 619 .BR send (2),
 620 .BR sendto (2),
 621 and
 622 .BR sendmsg (2).
 623 .IP *
 624 File locking interfaces:
 625 .BR flock (2)
 626 and
 627 .BR fcntl (2)
 628 .BR F_SETLKW .
 629 .IP *
 630 POSIX message queue interfaces:
 631 .BR mq_receive (3),
 632 .BR mq_timedreceive (3),
 633 .BR mq_send (3),
 634 and
 635 .BR mq_timedsend (3).
 636 .IP *
 637 .BR futex (2)
 638 .B FUTEX_WAIT
 639 (since Linux 2.6.22; beforehand, always failed with
 640 .BR EINTR ).
 641 .IP *
 642 POSIX semaphore interfaces:
 643 .BR sem_wait (3)
 644 and
 645 .BR sem_timedwait (3)
 646 (since Linux 2.6.22; beforehand, always failed with
 647 .BR EINTR ).
 648 .RE
 649 .PP
 650 The following interfaces are never restarted after
 651 being interrupted by a signal handler,
 652 regardless of the use of
 653 .BR SA_RESTART ;
 654 they always fail with the error
 655 .B EINTR
 656 when interrupted by a signal handler:
 657 .\" These are the system calls that give EINTR or ERESTARTNOHAND
 658 .\" on interruption by a signal handler.
 659 .RS 4
 660 .IP * 2
 661 Interfaces used to wait for signals:
 662 .BR pause (2),
 663 .BR sigsuspend (2),
 664 .BR sigtimedwait (2),
 665 and
 666 .BR sigwaitinfo (2).
 667 .IP *
 668 File descriptor multiplexing interfaces:
 669 .BR epoll_wait (2),
 670 .BR epoll_pwait (2),
 671 .BR poll (2),
 672 .BR ppoll (2),
 673 .BR select (2),
 674 and
 675 .BR pselect (2).
 676 .IP *
 677 System V IPC interfaces:
 678 .\" On some other systems, SA_RESTART does restart these system calls
 679 .BR msgrcv (2),
 680 .BR msgsnd (2),
 681 .BR semop (2),
 682 and
 683 .BR semtimedop (2).
 684 .IP *
 685 Sleep interfaces:
 686 .BR clock_nanosleep (2),
 687 .BR nanosleep (2),
 688 and
 689 .BR usleep (3).
 690 .IP *
 691 .BR read (2)
 692 from an
 693 .BR inotify (7)
 694 file descriptor.
 695 .IP *
 696 .BR io_getevents (2).
 697 .RE
 698 .PP
 699 The
 700 .BR sleep (3)
 701 function is also never restarted if interrupted by a handler,
 702 but gives a success return: the number of seconds remaining to sleep.
 703 .SS Interruption of System Calls and Library Functions by Stop Signals
 704 On Linux, even in the absence of signal handlers,
 705 certain blocking interfaces can fail with the error
 706 .BR EINTR
 707 after the process is stopped by one of the stop signals
 708 and then resumed via
 709 .BR SIGCONT .
 710 This behavior is not sanctioned by POSIX.1, and doesn't occur
 711 on other systems.
 712
 713 The Linux interfaces that display this behavior are:
 714 .RS 4
 715 .IP * 2
 716 .BR epoll_wait (2),
 717 .BR epoll_pwait (2).
 718 .IP *
 719 .BR semop (2),
 720 .BR semtimedop (2).
 721 .IP *
 722 .BR sigtimedwait (2),
 723 .BR sigwaitinfo (2).
 724 .IP *
 725 .BR read (2)
 726 from an
 727 .BR inotify (7)
 728 file descriptor.
 729 .IP *
 730 Linux 2.6.21 and earlier:
 731 .BR futex (2)
 732 .BR FUTEX_WAIT ,
 733 .BR sem_timedwait (3),
 734 .BR sem_wait (3).
 735 .IP *
 736 Linux 2.6.8 and earlier:
 737 .BR msgrcv (2),
 738 .BR msgsnd (2).
 739 .IP *
 740 Linux 2.4 and earlier:
 741 .BR nanosleep (2).
 742 .RE
 743 .SH "CONFORMING TO"
 744 POSIX.1, except as noted.
 745 .SH BUGS
 746 .B SIGIO
 747 and
 748 .B SIGLOST
 749 have the same value.
 750 The latter is commented out in the kernel source, but
 751 the build process of some software still thinks that
 752 signal 29 is
 753 .BR SIGLOST .
 754 .SH "SEE ALSO"
 755 .BR kill (1),
 756 .BR getrlimit (2),
 757 .BR kill (2),
 758 .BR killpg (2),
 759 .BR setitimer (2),
 760 .BR setrlimit (2),
 761 .BR sgetmask (2),
 762 .BR sigaction (2),
 763 .BR sigaltstack (2),
 764 .BR signal (2),
 765 .BR signalfd (2),
 766 .BR sigpending (2),
 767 .BR sigprocmask (2),
 768 .BR sigqueue (2),
 769 .BR sigsuspend (2),
 770 .BR sigwaitinfo (2),
 771 .BR abort (3),
 772 .BR bsd_signal (3),
 773 .BR longjmp (3),
 774 .BR raise (3),
 775 .BR sigset (3),
 776 .BR sigsetops (3),
 777 .BR sigvec (3),
 778 .BR sigwait (3),
 779 .BR strsignal (3),
 780 .BR sysv_signal (3),
 781 .BR core (5),
 782 .BR proc (5),
 783 .BR pthreads (7)