kill: Operation not permitted 具体与什么有关

不加其它参数的 kill 只是给进程发一个 TERM 信号，这个信号的意义，进程是可以自己定义的。

查到了 man 2 kill 中有说明
非特权进程需要 real user ID 或 effective user ID 等于目标进程的 real user ID 或 saved user ID 就有发送信号的权限
$ su -c "sleep 6m"
Password:
^Z
[1]+ Stopped su -c "sleep 6m"
$ bg
[1]+ su -c "sleep 6m" &
$ ps -o user,euser,ruser,suser,fuser,args --pid $!
USER EUSER RUSER SUSER FUSER COMMAND
root root nobody root root su -c sleep 6m
$ kill $!
$
Session terminated, killing shell... ...killed
[1]+ Terminated su -c "sleep 6m"
$ pkexec sleep 7m &
[1] 14472
$ ps -o user,euser,ruser,suser,fuser,args --pid $!
USER EUSER RUSER SUSER FUSER COMMAND
root root root root root /usr/bin/sleep 7m
$ kill $!
bash: kill: (14472) - Operation not permitted