How do I switch from an unknown shell to bash?

Question

I was surprised that I didn't find this question already on the site. So, today $ came up after I logged in as a new user. This was unexpected because my main user's prompt starts with username@computername:~$.

So, how do I switch from this other shell to bash?

Just because $ came up rather than username@computername:~$ doesn't mean it wasn't bash. The exact formatting of the prompt is set by the PS1 variable, which can be set up or customized differently for different users. — frabjous, Aug 30 '10 at 02:58
@mouche Re: @frabjous echo $SHELL to find out what your current shell is. — xenoterracide, Aug 30 '10 at 12:41
@mouche @frabjous and beginning with a $ is actually common for bash, some non bash shells like zsh use the % out of the box, I believe other shells use other things. — xenoterracide, Aug 30 '10 at 12:48
@xeno it was /bin/sh and something I tried to do didn't work like it would in BASH. — mouche, Aug 30 '10 at 16:15
@mouche being /bin/sh often doesn't mean much that's usually a symlink to something else. I'd type ls -l /bin/sh to see what it's a symlink to. In some cases being a symlink to something changes its behavior, I don't think bash is that way. — xenoterracide, Aug 30 '10 at 16:22
Oh, I never knew @xenoterracide. On my machine, /bin/sh is a symlink to /bin/dash. — mouche, Aug 31 '10 at 01:59
@xenoterracide - Using bash as /bin/sh disables many bash features (it goes into POSIX compliance mode). — Chris Down, Sep 24 '11 at 18:04
As Chris Down says, bash does behave differently in some ways when it sees it's been invoked as sh. It acts as though --norc was passed and it enters POSIX mode. — Eliah Kagan, Apr 24 '15 at 14:52

score 71 · Accepted Answer · edited Oct 30 '19 at 06:34

71

Assuming the unknown shell supports running an absolute command, you could try: /bin/bash

To change the default shell, I would use chsh(1). Sample usage: chsh -s /bin/bash $USER

edited Oct 30 '19 at 06:34

Pat Myron

103

answered Aug 30 '10 at 02:28

Kevin M

1,973

1

Does chsh permanently change the shell or just for the current session? – mouche Aug 30 '10 at 02:35
10

@mouche Permanently; it changes your entry in /etc/passwd – Michael Mrozek Aug 30 '10 at 02:36
@mouche, chsh(1) will only allow to change to a shell that is listed in /etc/shells (and is available, presumably). chsh -l lists the alternatives. Be careful, some (like nologin) are defined for accounts that should never be used to login (nice way to lock yourself out), there might be local additions for special uses. – vonbrand Feb 29 '16 at 15:56

score 20 · Answer 2 · edited May 20 '11 at 14:56

You type in bash. If you want this to be a permanent change the default shell to /bin/bash by editing /etc/passwd.

Here's some snippets from my /etc/passwd:

avahi:x:84:84:Avahi daemon:/:/bin/false
xenoterracide:x:1000:100::/home/xenoterracide:/bin/zsh
postgres:x:88:88::/var/lib/postgres:/bin/zsh
bob:x:1001:1001::/home/bob:/bin/bash
usbmux:x:140:140:usbmux user:/:/sbin/nologin

The very last field contains the shell, Modifying the field after the last : to a valid or invalid shell will work. /bin/false and /sbin/nologin both mean the user doesn't have a real login shell, although if pam is not set up right this doesn't mean they can't login (I reported a bug on this in Arch Linux, because you can login graphically without having a login shell). /bin/bash and /bin/zsh are both valid shells, see /etc/shells for a list of valid shells on your systems. Here's my /etc/shells if you're interested.

/bin/sh
/bin/bash
/bin/ksh
/bin/zsh
/bin/dash

Yes you can use chsh or usermod to do the same things, please remember these are just structured text files, and TIMTOWTDI.

You probably want to use chsh instead of manually editing passwd — Michael Mrozek, Aug 30 '10 at 02:38
@Michael there are about 5 (POOMA) different ways to change the shell in /etc/passwd I didn't feel like listing any of them, because I always do it manually. chsh and usermod can both do it. — xenoterracide, Aug 30 '10 at 12:27
Messing around with configuration files is a Bad Idea(TM), an error might make the system unusable. Yes, it is often the only/fastest way, but then do it with *extreme care*. — vonbrand, Feb 29 '16 at 15:58

score 16 · Answer 3 · answered Aug 30 '10 at 20:05

16

If chsh or manually editing the config won't work, but a ~/.profile script is executed at login, add this line:

exec /bin/bash --login

answered Aug 30 '10 at 20:05

Kevin Cantu

3,794

After looking around for a while, this was the solution I needed. Thanks! – PearsonArtPhoto Aug 08 '12 at 13:13
Great idea, specially if the shell selected sources that file on startup... – vonbrand Feb 29 '16 at 15:59
3

touch ~/.bash_profile or otherwise bash will exec itself in a loop: bash takes ~/.profile in case ~/.bash_profile doesn't exist. – alephreish Dec 31 '17 at 14:44

How do I switch from an unknown shell to bash?

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