What does the 'sudo -s' command do, and how is it used in this example?
The simple answer is it gives you a root shell. That's what it's being used for here. There's a good technical comparison between the su
, sudo -i
, sudo -s
and sudo su
methods on Unix.SE but that's really not relevant here. The code could have used any and would have worked.
The help nugget means a few things:
It's looking for a command in the
$SHELL
environment variable. If you runecho $SHELL
you'll probably see/bin/bash
. That means you'll get a root instance of Bash. I'm sure if you were inzsh
it would mean you get a root instance ofzsh
.If
$SHELL
is empty, it falls back to the default shell defined in/etc/passwd
for that user.If you provide a command (eg
sudo -s whoami
), it's actually running:sudo /bin/bash -c "whoami"
If you don't pass a command, it doesn't pass a
-c
argument over so you just get an interactive shell.
I've used the phrase "root" several times. By default sudo
is all about running things as root but sudo
(and su) can run things as other users (if you have permission to do so). I'm only stating this for the pedants who will cry out that sudo -s -u $USER
doesn't give them a root shell as I promised -s
would above.
And in my humblest of opinions, it's really silly to become root for just two commands, not to mention that it could leave a user accidentally running further commands as root. If you want or need to run something as root, just premend the command with sudo
:
sudo apt-get update
sudo apt-get install -y build-essential libtool libcurl4-openssl-dev libncurses5-dev libudev-dev autoconf automake screen
I'd be dubious of any tutorial that suggested getting a root shell, except in the cases where you do have bucketloads of commands to run... And even then, there's scripting.
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AndreaNobili
Updated on September 18, 2022Comments
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AndreaNobili over 1 year
I have the following doubt. In a tutorial related to a software installation that I am following say that I have to execute the following commands (I am doing it into an ssh shell, so this list of steps end with the
exit
command):sudo -s apt-get update apt-get install -y build-essential libtool libcurl4-openssl-dev libncurses5-dev libudev-dev autoconf automake screen exit
My doubts are:
What exactly does the
-s
parameter do aftersudo
command?Searching on the web I found that:
‑s [command] The ‑s (shell) option runs the shell specified by the SHELL environment variable if it is set or the shell as specified in the password database. If a command is specified, it is passed to the shell for execution via the shell's ‑c option. If no command is specified, an interactive shell is executed
It seems to me that the
sudo -s
execute a command using the environment variable of the shell.But this is not clear for me: in this case what is the command executed with the environment variable? (it only executes
sudo -s
and notsudo -s [command]
). -
AndreaNobili almost 10 yearsPerfect explaination. Now it is all more clear. One last doubt. If I preappend sudo to all the previous commands I will obtain the same final result? is it true or am I missing something?
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RCF almost 10 years@Oli you are 100% correct about Zsh, "sudo -s" logs into a "root" shell as "root" not Super User.
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Oli almost 10 years@AndreaNobili Yeah, that's what
sudo
is generally for; running a command as root without having to manually log in as root. -
WinEunuuchs2Unix over 4 yearsFYI I posted an answer below yours and my take on
sudo -s
is drastically different because of my limited knowledge and happening across the situation by accident. Still you might want to read my "humble" answer and possibly refresh your 1/2 decade old answer.