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This article mainly explains "what is the function of Linux signal list". Interested friends may wish to have a look at it. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "what is the function of Linux signal list"?

We run the following command to see a list of signals supported by Linux:

~ $kill-l

1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL

5) SIGTRAP 6) SIGABRT 7) SIGBUS 8) SIGFPE

9) SIGKILL 10) SIGUSR1 11) SIGSEGV 12) SIGUSR2

13) SIGPIPE 14) SIGALRM 15) SIGTERM 17) SIGCHLD

18) SIGCONT 19) SIGSTOP 20) SIGTSTP 21) SIGTTIN

22) SIGTTOU 23) SIGURG 24) SIGXCPU 25) SIGXFSZ

26) SIGVTALRM 27) SIGPROF 28) SIGWINCH 29) SIGIO

30) SIGPWR 31) SIGSYS 34) SIGRTMIN 35) SIGRTMIN+1

36) SIGRTMIN+2 37) SIGRTMIN+3 38) SIGRTMIN+4 39) SIGRTMIN+5

40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8 43) SIGRTMIN+9

44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13

48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13

52) SIGRTMAX-12 53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9

56) SIGRTMAX-8 57) SIGRTMAX-7 58) SIGRTMAX-6 59) SIGRTMAX-5

60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2 63) SIGRTMAX-1

64) SIGRTMAX

In the list, the signal numbered 1-31 is supported by traditional UNIX and is unreliable (non-real-time), while the signal numbered 32-63 is later expanded and called reliable signal (real-time signal). The difference between an unreliable signal and a reliable signal is that the former does not support queuing, which may cause signal loss, while the latter does not.

Let's discuss the signal whose number is less than SIGRTMIN.

1) SIGHUP

This signal is sent at the end of the user terminal connection (normal or abnormal), usually at the end of the control process of the terminal, notifying each job in the same session, when they are no longer associated with the control terminal.

When logging in to Linux, the system assigns a terminal (Session) to the logged-in user. All programs running on this terminal, including foreground process group and background process group, generally belong to this Session. When the user logs out of Linux, the foreground process group and the process with output to the terminal in the background will receive the SIGHUP signal. The default operation of this signal is to terminate the process, so the process with terminal output in the foreground and background will be aborted. However, you can capture this signal, for example, wget can capture the SIGHUP signal and ignore it, so that even if you log out of the Linux login, wget can continue to download.

In addition, for daemons that are disconnected from the terminal, this signal is used to tell it to reread the configuration file.

2) SIGINT

A program termination (interrupt) signal that is sent when the user types an INTR character (usually Ctrl-C) to notify the foreground process group to terminate the process.

3) SIGQUIT

Similar to SIGINT, but controlled by QUIT characters (usually Ctrl-\). The process generates a core file when it receives a SIGQUIT exit, which is similar to a program error signal in this sense.

4) SIGILL

Illegal instructions were carried out. It is usually due to an error in the executable itself or an attempt to execute a data segment. This signal can also be generated when the stack overflows.

5) SIGTRAP

Generated by breakpoint instructions or other trap instructions. Used by debugger.

6) SIGABRT

The signal generated by calling the abort function.

7) SIGBUS

Illegal address, including memory address alignment (alignment) error. For example, access to a four-word integer whose address is not a multiple of 4. It differs from SIGSEGV in that the latter is triggered by illegal access to legitimate storage addresses (such as access that does not belong to its own storage space or read-only storage space).

8) SIGFPE

Issued when a fatal arithmetic error occurs. It includes not only floating-point arithmetic errors, but also all other arithmetic errors such as overflows and divisor 0.

9) SIGKILL

It is used to end the running of the program immediately. This signal cannot be blocked, processed or ignored. If the administrator finds that a process cannot be terminated, try to send this signal.

10) SIGUSR1

Leave it to the user

11) SIGSEGV

Try to access memory that is not allocated to you, or try to write data to a memory address that does not have write permission.

12) SIGUSR2

Leave it to the user

13) SIGPIPE

The pipe is broken. This signal is usually generated in inter-process communication, such as two processes using FIFO (pipeline) communication. If the read pipeline is not opened or terminated unexpectedly, the write process will receive the SIGPIPE signal. In addition, the two processes that communicate with Socket, the write process, the read process has been terminated while writing the Socket.

14) SIGALRM

Clock timing signal, which calculates the actual time or clock time. The alarm function uses this signal.

15) SIGTERM

Program end (terminate) signal, unlike SIGKILL, which can be blocked and processed. It is usually used to require the program to exit normally, and the shell command kill generates this signal by default. If the process cannot be terminated, we will try SIGKILL.

17) SIGCHLD

When the child process ends, the parent process receives this signal.

If the parent process does not process this signal and does not wait the child process, the child process terminates, but it still occupies the table item in the kernel process table, and the child process is called a zombie process. This situation should be avoided (the parent process either ignores the SIGCHILD signal, or captures it, or wait its derived child process, or the parent process terminates first, where the termination of the child process is automatically taken over by the init process).

18) SIGCONT

Allow a stopped (stopped) process to continue. This signal cannot be blocked. You can use a handler to get a program to do specific work when it changes from stopped state to continue execution. For example, redisplay the prompt

19) SIGSTOP

Stop the execution of the stopped process. Note the difference between it and terminate and interrupt: the process is not finished, it is just paused. This signal cannot be blocked, processed or ignored.

20) SIGTSTP

Stop the process, but the signal can be processed and ignored. This signal is sent when the user types the SUSP character (usually Ctrl-Z)

21) SIGTTIN

When a background job reads data from a user terminal, all processes in the job receive SIGTTIN signals. By default, these processes stop execution.

22) SIGTTOU

Similar to SIGTTIN, but received when writing to a terminal (or modifying terminal mode).

23) SIGURG

"urgent" data or out-of-band data is generated when it arrives at socket.

24) SIGXCPU

CPU time resource limit exceeded. This limit can be read / changed by getrlimit/setrlimit.

25) SIGXFSZ

When the process attempts to expand the file so as to exceed the file size resource limit.

26) SIGVTALRM

Virtual clock signal. Similar to SIGALRM, but calculates the CPU time consumed by the process.

27) SIGPROF

Similar to SIGALRM/SIGVTALRM, but including the CPU time used by the process and the time of system calls.

28) SIGWINCH

Issued when the window size changes.

29) SIGIO

The file descriptor is ready to start input / output operations.

30) SIGPWR

Power failure

31) SIGSYS

Illegal system call.

Among the signals listed above, the signals that cannot be captured, blocked or ignored by the program are: SIGKILL,SIGSTOP

The signals that cannot be restored to the default action are: SIGILL,SIGTRAP

By default, the signal that causes the process to abort is: SIGABRT,SIGBUS,SIGFPE,SIGILL,SIGIOT,SIGQUIT,SIGSEGV,SIGTRAP,SIGXCPU,SIGXFSZ

The default signal that causes the process to exit is: SIGALRM,SIGHUP,SIGINT,SIGKILL,SIGPIPE,SIGPOLL,SIGPROF,SIGSYS,SIGTERM,SIGUSR1,SIGUSR2,SIGVTALRM

The default signal that causes the process to stop is: SIGSTOP,SIGTSTP,SIGTTIN,SIGTTOU

The signals ignored by the default process are: SIGCHLD,SIGPWR,SIGURG,SIGWINCH

In addition, SIGIO exits in SVR4 and is ignored in 4.3BSD; SIGCONT continues when the process is suspended, otherwise it is ignored and cannot be blocked.

The following are the supplements of other netizens:

SIGHUP terminating process terminal line hangs up

SIGINT terminates process interrupts process

SIGQUIT sets up a CORE file to terminate the process, and generates a core file

Illegal instruction for SIGILL to establish CORE file

SIGTRAP sets up CORE file tracking traps

SIGBUS error establishing CORE file bus

Illegal error creating CORE file segment in SIGSEGV

SIGFPE creates floating point exception in CORE file

SIGIOT establishes the CORE file and executes Irambo self-trapping.

SIGKILL terminates the process and kills the process

SIGPIPE terminates the process to write data to a pipe that does not read the process.

When the SIGALARM termination process timer arrives

SIGTERM termination process software termination signal

SIGSTOP stop process stop signal from non-terminal

Stop signal from SIGTSTP stop process terminal

SIGCONT ignores the signal to continue with a stopped process

SIGURG ignores the signal I am O emergency signal

SIGIO ignores that the signal descriptor can be used to perform Icano.

SIGCHLD ignores the signal to notify the parent process when the child process stops or exits

SIGTTOU stop process background process write terminal

SIGTTIN stop process background process read terminal

SIGXGPU terminates the process CPU timeout

SIGXFSZ termination process file length is too long

SIGWINCH ignores the change in signal window size

The statistical distribution map of SIGPROF termination process arrives with timer.

SIGUSR1 terminates the process user-defined signal 1

SIGUSR2 terminates the process user-defined signal 2

SIGVTALRM terminates the process when the virtual timer arrives

1) SIGHUP this signal is sent at the end of the user terminal connection (normal or abnormal), usually in the terminal control

When the manufacturing process ends, each job in the same session is notified, and then they are in conjunction with the control terminal.

No longer related.

2) SIGINT program termination (interrupt) signal, which is sent when the user types the INTR character (usually Ctrl-C)

3) SIGQUIT is similar to SIGINT, but is controlled by QUIT characters (usually Ctrl-). The process is due to receipt

A core file is generated when SIGQUIT exits, which is similar to a program error message in this sense.

No.

4) SIGILL executed illegal instructions. It is usually due to an error in the executable itself or an attempt to execute the

Data segment. This signal may also be generated when the stack is overflowed.

5) SIGTRAP is generated by breakpoint instructions or other trap instructions. Used by debugger.

6) it occurs when the SIGABRT program finds an error and calls abort.

6) SIGIOT is generated by the iot instruction on PDP-11, just like SIGABRT on other machines.

7) illegal SIGBUS address, including memory address alignment (alignment) error. Eg: access a four-word length

Is an integer, but its address is not a multiple of 4.

8) SIGFPE is issued when a fatal arithmetic error occurs. Includes not only floating-point arithmetic errors, but also overflow

All other arithmetic errors such as out and divisor 0.

9) SIGKILL is used to immediately end the running of the program. This signal cannot be blocked, processed or ignored.

10) SIGUSR1 is reserved for users

11) SIGSEGV attempts to access memory that is not allocated to it, or attempts to write data to a memory address that does not have write permission.

12) SIGUSR2 is reserved for users

13) SIGPIPE Broken pipe

14) SIGALRM clock timing signal, which calculates the actual time or clock time. The alarm function uses the

Signal.

15) SIGTERM program end (terminate) signal, which, unlike SIGKILL, can be blocked and

Deal with. It is usually used to require the program to exit normally. The shell command kill produces this by default

A signal.

17) when the SIGCHLD child process ends, the parent process receives this signal.

18) SIGCONT allows a stopped process to continue execution. This signal cannot be blocked. Can be used

A handler to allow the program to complete a specific when the stopped state changes to continue execution

Work. For example, redisplay the prompt

19) SIGSTOP stops (stopped) the execution of the process. Notice the difference between it and terminate and interrupt:

The process is not over yet, it is just suspended. This signal cannot be blocked, processed or ignored.

20) SIGTSTP stops the process, but the signal can be processed and ignored. When the user types the SUSP character

(usually Ctrl-Z) send this signal

21) SIGTTIN when a background job wants to read data from a user terminal, all processes in the job will receive SIGTTIN

Signal. By default, these processes stop execution.

22) SIGTTOU is similar to SIGTTIN, but is received when writing to the terminal (or modifying the terminal mode).

23) SIGURG has "urgent" data or out-of-band data that is generated when it arrives at socket.

24) SIGXCPU exceeds the time resource limit of CPU. This limit can be read by getrlimit/setrlimit /

Change

25) SIGXFSZ exceeds the file size resource limit.

26) SIGVTALRM virtual clock signal. Similar to SIGALRM, but calculates the CPU time consumed by the process.

27) SIGPROF is similar to SIGALRM/SIGVTALRM, but includes the CPU time used by the process and the

time。

28) issued when the size of the SIGWINCH window changes.

29) the SIGIO file descriptor is ready to start input / output operations.

30) SIGPWR Power failure

There are two signals to stop the process: SIGTERM and SIGKILL. SIGTERM is friendly, and the process can catch this signal and close the program according to your needs. Before closing the program, you can end the open record file and complete the tasks you are doing. In some cases, if the process is working and cannot be interrupted, the process can ignore this SIGTERM signal.

For SIGKILL signals, the process cannot be ignored. This is a signal that "I don't care what you're doing, stop right now". If you send a SIGKILL signal to the process, Linux stops the process there.

At this point, I believe you have a deeper understanding of "what is the role of Linux signal list". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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