Meaning of the return value when the Linux program exits

# Define sighup 1
The process is caused by the control terminal dead or the control terminal issuing a command
# Define SIGINT 2
Signal generated by keyboard interruption

# Define sigquit 3
Keyboard termination

# Define sigill 4
Invalid Command

# Define sigtrap 5
A process encounters a trace or an interrupt nesting

# Define SIGABRT 6
Interrupt signal generated by the abort system call

# Define sigiot 6
Similar to SIGABRT

# Define sigbus 7
The process tries to use unreasonable memory

# Define sigfpe 8
Floating Point exception

# Define sigkill 9
Kill

# Define SIGUSR1 10
User-Defined

# Define SIGSEGV 11
Segment Error

# Define sigusr2 12
User-Defined

# Define sigpipe 13
No read-only writes during pipeline operations

# Define sigalrm 14
Timer clock signal generated by alarm system call

# Define sigterm 15
Processes that receive terminal Signals

# Define sigstkflt 16
Stack Error

# Define sigchld 17
Signal that the child process has stopped or ended to the parent process

# Define sigcont 18
Continue running Signal

# Define sigstop 19
Stop

# Define sigtstp 20
The stop signal generated by the keyboard

# Define sigttin 21
Stdin data needs to be read when running in the post status

# Define sigttou 22
When running in the back state, you need to write to stdout

# Define sigurg 23
Socket emergency

# Define sigxcpu 24
The time when the process exceeds the CPU allocation limit.

# Define sigxfsz 25
The process uses a file that exceeds the length specified by the system.

# Define sigvtalrm 26
Internal alarm clock expired

# Define sigprof 27
Depicts the expiration of a clock set in a program segment

# Define sigwinch 28
Terminal window changes

# Define sigio 29
Non-synchronous Io

# Define sigpoll sigio
Pollable event occurred