I mistakenly entered
chsh -s /usr/bin
instead of
chsh -s /bin/bash
and now I can't log into a root shell, how do I start a bash shell as root manually ?
asked Mar 28, 2016 at 13:11
5 Answers
While root does not have access, a user in the sudo group can still run privileged commands - it seems the error is not in sudo, but elsewhere in the sudo chshcommand (e.g. chsh error).
As such your sudo is apparently working.
The passwd file can be edited with:
sudo vipw
And the root shell changed manually.
(first line of /etc/passwd usually)
root:x:0:0:root:/root:/bin/bash
Fom man vipw
The vipw and vigr commands edits the files /etc/passwd and /etc/group, respectively. With the -s flag, they will edit the shadow versions of those files, /etc/shadow and /etc/gshadow, respectively. The programs will set the appropriate locks to prevent file corruption.
answered Mar 28, 2016 at 13:34
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3I never knew about
vipwandvigr, thank you! I always usedsudo vim /etc/passwd– catMar 28, 2016 at 15:54 -
3You might be interested in
visudosudo.ws/man/1.8.15/visudo.man.html too, @tac Mar 28, 2016 at 16:05 -
3
Another option, assuming you have access to another account, is to manually override the default shell by using su --shell=/bin/bash:
-s, --shell=SHELL
run SHELL if /etc/shells allows it
The primary advantage of this is that it only requires access to another account, not another privileged one.
For security reasons, logins whether textual or graphical and utilities like su and sudo that allow you to run commands as a different user all run those command through the target user's shell. If the target user's shell is non-functional, well, you've seen the results :-(
Unless you happen to have a still-functional root shell running somewhere or something like a setuid-root binary or something that allows you to bypass this, rebooting and correcting the problem using a rescue system or live image is probably your best bet.
Boot the rescue system, mount your real system's root filesystem somewhere, say, /mnt/foo, and edit /mnt/foo/etc/passwd to fix the shell. Save, unmount, and you're done.
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curious, what happens if you do this and the /etc/passwd file is in a hash instead of plain text?– jgr208Mar 28, 2016 at 13:18
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1
/etc/passwdis not plaintext? I haven't seen that in at least, like, a decade. Is that still a thing on some systems? Anyway, I guesschroot /mnt/foo chsh -s /bin/bashmight do the trick in that case?– CeladaMar 28, 2016 at 13:21 -
I have never had the problem described, however I work with locked down systems that need to have /etc/passwd not in plain text as to avoid hackers and the such compromising the system even more if they gain access. Hmm that might work, lets just say I hope i never have to try and see if it works actually.– jgr208Mar 28, 2016 at 13:24
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I was able to edit /etc/passwd with sudo from a user account, I wasn't aware that the shell was defined in this file, thanks Mar 28, 2016 at 13:34
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@ChiseledAbs oh, you were? Good for you, glad you solved your problem. I didn't think it would let you.– CeladaMar 28, 2016 at 13:36
Add init=/bin/bash to your kernel command line ( if booting with grub, press e to edit the boot entry ), and you will have a bash shell running as root without even having to supply a password. Your root filesystem likely will still be mounted read only though, so you will need to remount it first, then you can change the shell back with chsh.
sudo usermod -s /bin/bash jdoe
will change the shell of jdoe to bash. You can then sudo egrep jdoe /etc/passwd to verify.
answered Mar 29, 2016 at 1:30
sudo vipwwork?