What happens when I sudo bash -c? [closed]

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Closed 3 years ago.

I know that sudo bash -c 'some_command' will run some_command with the same privileges as sudo.

I'm confused as to what's happening? Does it run some_command in bash as sudo (same as sudo bash) then switch back to my current user? Why am I not left in an instance of bash with sudo privileges like I would when I run sudo bash?

I tried running man bash and it describes the -c option (quoted below). However, I am struggling to piece how the description relates to the behaviour I observed when running sudo bash -c 'some_command'

If the -c option is present, then commands are read from the first non-option argument command_string. If there are arguments after the command_string, they are assigned to the positional parameters, starting with $0.

回答1:

sudo switches users and then executes bash, passing it the other arguments. bash running as the new user runs the command in the argument after -c.

回答2:

Consider this snippet (pay attention to UID & PID/PPID columns.):

$ sudo ps -f
UID        PID  PPID  C STIME TTY          TIME CMD
root      8997  8715  0 11:57 pts/17   00:00:00 sudo ps -f
root      8998  8997  0 11:57 pts/17   00:00:00 ps -f

$ sudo bash -c 'ps -f'
UID        PID  PPID  C STIME TTY          TIME CMD
root      8909  8715  3 11:55 pts/17   00:00:00 sudo bash -c ps -f
root      8910  8909  0 11:55 pts/17   00:00:00 ps -f

$ sudo bash -c 'echo hi; ps -f'
hi
UID        PID  PPID  C STIME TTY          TIME CMD
root      8957  8715  0 11:56 pts/17   00:00:00 sudo bash -c echo hi; ps -f
root      8958  8957  0 11:56 pts/17   00:00:00 bash -c echo hi; ps -f
root      8959  8958  0 11:56 pts/17   00:00:00 ps -f

1. In 1st case, sudo starts ps -f as root user.
2. In 2nd case, sudo starts bash as root user with arguments -c 'ps -f'. It appears that as an optimization, bash is using exec to start ps -f. Hence, only 2 processes are seen.
3. In 3rd case, sudo starts bash as root user with arguments -c 'echo hi; ps -f'. The command (argument to -c) is not a simple executable + args. They are 2 commands separated by ;. So, bash cannot call exec directly. It uses the standard fork+exec mechanism. So, bash is the parent of the ps process.

来源：https://stackoverflow.com/questions/37851390/what-happens-when-i-sudo-bash-c