Talk:Shell
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==What is a login shell?== | ==What is a login shell?== | ||
| − | I was a Slackware user for some time, before finding FreeBSD. One of the things that surprised me was that FreeBSD seems to be | + | I was a Slackware user for some time, before finding FreeBSD. <s>One of the things that surprised me was that FreeBSD seems to be fuzzier about what a login shell is.</s> Slackware, and I suppose any linux, has a shell database (<code>/etc/shells</code>). If you attempt to change shells as an ordinary user, to provide a different login shell, it must exist in the shell database. <s>As far as I can tell, there is no such restriction in FreeBSD even though it also has a shell database.</s> In fact, (as <code>root</code>) any program at all can be substituted for a shell in the Shell field of the user's login profile (<code>/etc/passwd</code>), as long as it exists in the global PATH (only root can specify non-standard shells - such as <code>/usr/sbin/nologin</code>). |
%grep python /etc/passwd | %grep python /etc/passwd | ||
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</pre> | </pre> | ||
| − | Useless, but interesting, eh? Here, the user's login shell is <code>/usr/local/bin/python</code>. Needless to say, that file is not listed in <code>/etc/shells</code>. When does FreeBSD use the shell database? — [[User:Ninereasons|Ninereasons]] 13:07, 7 June 2006 (EDT) | + | Useless, but interesting, eh? Here, the user's login shell is <code>/usr/local/bin/python</code>. Needless to say, that file is not listed in <code>/etc/shells</code>. When does FreeBSD use the shell database, if logged in as root? Maybe Linux works the same, but I just never noticed? — [[User:Ninereasons|Ninereasons]] 13:07, 7 June 2006 (EDT) |
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| + | : It's true. I never noticed. Linux works just like this also. So, lftp, or cpan or the like, could be my login shell. Weird. [[User:Ninereasons|Ninereasons]] 02:48, 9 June 2006 (EDT) | ||
Latest revision as of 14:24, 9 June 2006
[edit] What is a login shell?
I was a Slackware user for some time, before finding FreeBSD. One of the things that surprised me was that FreeBSD seems to be fuzzier about what a login shell is. Slackware, and I suppose any linux, has a shell database (/etc/shells). If you attempt to change shells as an ordinary user, to provide a different login shell, it must exist in the shell database. As far as I can tell, there is no such restriction in FreeBSD even though it also has a shell database. In fact, (as root) any program at all can be substituted for a shell in the Shell field of the user's login profile (/etc/passwd), as long as it exists in the global PATH (only root can specify non-standard shells - such as /usr/sbin/nologin).
%grep python /etc/passwd pylogin:*:2011:2011:Login to python:/home/pylogin:/usr/local/bin/python
I don't know what might be the full implications; but it is somewhat surprising that it's possible to have a ssh session that looks like this:
Using username "pylogin".
Using keyboard-interactive authentication.
Password:
Last login: Wed Jun 7 09:37:40 2006 from kanga
Copyright (c) 1980, 1983, 1986, 1988, 1990, 1991, 1993, 1994
The Regents of the University of California. All rights reserved.
FreeBSD 6.1-STABLE (GENERIC) #10: Mon Jun 5 09:57:27 PDT 2006
Welcome to FreeBSD AMD64!
Python 2.4.3 (#2, Apr 6 2006, 15:45:31)
[GCC 3.4.4 [FreeBSD] 20050518] on freebsd6
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> keys = os.environ.keys()
>>> for val in keys:
... print val,": ",os.environ[val]
...
TERM : xterm
SHELL : /usr/local/bin/python
MAIL : /var/mail/pylogin
BLOCKSIZE : K
FTP_PASSIVE_MODE : YES
SSH_TTY : /dev/ttyp5
SSH_CLIENT : 192.168.1.3 3173 22
LOGNAME : pylogin
USER : pylogin
HOME : /home/pylogin
PATH : /sbin:/bin:/usr/sbin:/usr/bin:/usr/games:/usr/local/sbin:/usr/local/bin:/usr/X11R6/bin:/home/pylogin/bin
SSH_CONNECTION : 192.168.1.3 3173 192.168.1.5 22
>>> ^d
Useless, but interesting, eh? Here, the user's login shell is /usr/local/bin/python. Needless to say, that file is not listed in /etc/shells. When does FreeBSD use the shell database, if logged in as root? Maybe Linux works the same, but I just never noticed? — Ninereasons 13:07, 7 June 2006 (EDT)
- It's true. I never noticed. Linux works just like this also. So, lftp, or cpan or the like, could be my login shell. Weird. Ninereasons 02:48, 9 June 2006 (EDT)
