What signal 0 does in kill command?

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wx5bcd90b347f01 2021-10-25 15:05:29

环境

Red Hat Enterprise Linux 6.4
util-linux

问题

What signal 0 does in kill command?
when I execute "kill -0 PID" and PID is the id of a thread, the command exit without errors.

[root@host ~]# ps -eo pid,comm|grep -c 10252
0

[root@host ~]# kill -0 10252;echo $?
0

[root@host ~]# cat /proc/18020/task/10252/stat
10252 (imsd) S 1 18020 18020 0 -1 4202560 4 0 0 0 2 1 0 0 19 -1 1351 0 987845280 615174144 118443 18446744073709551615 134512640 139793320 4286914320 3934351508 4151395376 0 16391 4096 16391 18446744071580550505 0 0 -1 8 0 0 3 0 0

Is that the correct behavior of kill -0 command ?

决议

From the man page of kill,

Raw

              If sig is 0, then no signal is sent, but error checking is still performed.

This means, it just checks errors, doesn't kill the process.

Raw

[root@example~]# ps aux  | grep rsyslog
root      1117  0.0  0.2 1077544 42684 ?       Ssl  06:02   0:02 /sbin/rsyslogd -n
root      8196  0.0  0.0 112680  2248 pts/0    S+   13:24   0:00 grep --color=auto rsyslog

[root@example~]# kill -0 1117

[root@example~]# echo $?
0

[root@example~]# ps aux  | grep rsyslog
root      1117  0.0  0.2 1077544 42684 ?       Ssl  06:02   0:02 /sbin/rsyslogd -n
root      8198  0.0  0.0 112680  2184 pts/0    S+   13:24   0:00 grep --color=auto rsyslog