ls -all $(which pidof)，结果如下：
lrwxrwxrwx 1 root root 14 May 19 2021 /usr/bin/pidof -> /sbin/killall5
pidof is actually the same program as killall5; the program behaves according to the name under which it is called.
When pidof is invoked with a full pathname to the program it should find the pid of, it is reasonably safe. Otherwise it is possible that it returns pids of running programs that happen to have the same name as the program you’re after but are actually other programs. Note that that the executable name of running processes is calculated with readlink(2), so symbolic links to executables will also match.
/* Get program name. */
strace pidof 1：
openat(AT_FDCWD, "156204/stat", O_RDONLY) = 4