Resource Management
Monitor system resources.
top
htopIf a process is killed, it returns a negative number. The number corresponds to the type of signal used to kill it.
POSIX signals:
man signal
man 7 signalSignal numbers from man 7 signal:
Standard signals
Linux supports the standard signals listed below. The second column of the table indi‐
cates 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.
Signal Standard Action Comment
────────────────────────────────────────────────────────────────────────
SIGABRT P1990 Core Abort signal from abort(3)
SIGALRM P1990 Term Timer signal from alarm(2)
SIGBUS P2001 Core Bus error (bad memory access)
SIGCHLD P1990 Ign Child stopped or terminated
SIGCLD - Ign A synonym for SIGCHLD
SIGCONT P1990 Cont Continue if stopped
SIGEMT - Term Emulator trap
SIGFPE P1990 Core Floating-point exception
SIGHUP P1990 Term Hangup detected on controlling terminal
or death of controlling process
SIGILL P1990 Core Illegal Instruction
SIGINFO - A synonym for SIGPWR
SIGINT P1990 Term Interrupt from keyboard
SIGIO - Term I/O now possible (4.2BSD)
SIGIOT - Core IOT trap. A synonym for SIGABRT
SIGKILL P1990 Term Kill signal
SIGLOST - Term File lock lost (unused)
SIGPIPE P1990 Term Broken pipe: write to pipe with no
readers; see pipe(7)
SIGPOLL P2001 Term Pollable event (Sys V);
synonym for SIGIO
SIGPROF P2001 Term Profiling timer expired
SIGPWR - Term Power failure (System V)
SIGQUIT P1990 Core Quit from keyboard
SIGSEGV P1990 Core Invalid memory reference
SIGSTKFLT - Term Stack fault on coprocessor (unused)
SIGSTOP P1990 Stop Stop process
SIGTSTP P1990 Stop Stop typed at terminal
SIGSYS P2001 Core Bad system call (SVr4);
see also seccomp(2)
SIGTERM P1990 Term Termination signal
SIGTRAP P2001 Core Trace/breakpoint trap
SIGTTIN P1990 Stop Terminal input for background process
SIGTTOU P1990 Stop Terminal output for background process
SIGUNUSED - Core Synonymous with SIGSYS
SIGURG P2001 Ign Urgent condition on socket (4.2BSD)
SIGUSR1 P1990 Term User-defined signal 1
SIGUSR2 P1990 Term User-defined signal 2
SIGVTALRM P2001 Term Virtual alarm clock (4.2BSD)
SIGXCPU P2001 Core CPU time limit exceeded (4.2BSD);
see setrlimit(2)
SIGXFSZ P2001 Core File size limit exceeded (4.2BSD);
see setrlimit(2)
SIGWINCH - Ign Window resize signal (4.3BSD, Sun)
The signals SIGKILL and SIGSTOP cannot be caught, blocked, or ignored.
Up to and including Linux 2.2, the default behavior for SIGSYS, SIGXCPU, SIGXFSZ, and (on
architectures other than SPARC and MIPS) SIGBUS was to terminate the process (without a
core dump). (On some other UNIX systems the default action for SIGXCPU and SIGXFSZ is to
terminate the process without a core dump.) Linux 2.4 conforms to the POSIX.1-2001 re‐
quirements for these signals, terminating the process with a core dump.
SIGEMT is not specified in POSIX.1-2001, but nevertheless appears on most other UNIX sys‐
tems, where its default action is typically to terminate the process with a core dump.
SIGPWR (which is not specified in POSIX.1-2001) is typically ignored by default on those
other UNIX systems where it appears.
SIGIO (which is not specified in POSIX.1-2001) is ignored by default on several other
UNIX systems.Signal numbering from man 7 signal:
Signal numbering for standard signals
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 architec‐
tures; 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 architec‐
ture.
Signal x86/ARM Alpha/ MIPS PARISC Notes
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:
* Where defined, SIGUNUSED is synonymous with SIGSYS. Since glibc 2.26, SIGUNUSED is no
longer defined on any architecture.
* Signal 29 is SIGINFO/SIGPWR (synonyms for the same value) on Alpha but SIGLOST on
SPARC.Last updated