Su problems

Message

csfsmash · Post by **csfsmash** » Sat May 20, 2006 1:40 am

i got this error :O

smash ~ $ su
/bin/sh: Permission denied

how i fix this?

roseZ · Post by **roseZ** » Sat May 20, 2006 5:34 am

It looks like root's shell is set to /bin/sh in /etc/passwd, and the execute permission to /bin/sh (or to whatever it points to, if it's a symlink) is not set.

csfsmash · Post by **csfsmash** » Sat May 20, 2006 5:59 am

So, what i have to do to fix the problem?

roseZ · Post by **roseZ** » Sat May 20, 2006 6:12 am

Check what /bin/sh looks like by

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ls -l /bin/sh

For me, the output looks like this

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lrwxrwxrwx 1 root root 4 Apr 16 21:37 /bin/sh -> bash

which means that /bin/sh is a symlink pointing to /bin/bash. In this case, do the same thing for the link's target. In my case this is

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ls -l /bin/bash

which outputs

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-rwxr-xr-x 1 root root 767264 Apr 16 21:37 /bin/bash

Now, the critical parts are those x's. To set permissions like this issue (as root)

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chmod 0755 /bin/bash

You can make yourself root without su, right?

csfsmash · Post by **csfsmash** » Sat May 20, 2006 3:01 pm

ii did what you told and i still gettint permission denied...
as root i can run the su command.. for example
localhost ~ # su smash
smash@localhost /root $

any idea?

overkll · Post by **overkll** » Sat May 20, 2006 3:21 pm

Did you add the user that you are using to issue su to the "wheel" group?

gentoo_dude · Post by **gentoo_dude** » Sat May 20, 2006 3:41 pm

Wheel group is to be able to perfom commands using sudo (as root).
su is to become another user if you know the user's password.

Do a ls -lsa /bin/su or ls -lsa /usr/bin/su.
See what group can do su. Add your user account to that group.

Mine is like this:

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28 -rws--x--x 1 root root 25024 Mar 17 16:12 /bin/su

Looks like it has the sticky bit set for uid. That means it will run with root previledges whoever runs that command. Probably the sticky bit has been reset.
In order to change it back you have to do

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chmod 4711 /bin/su

csfsmash · Post by **csfsmash** » Sat May 20, 2006 4:06 pm

i got 21 -wrwxr-xr-x 1 root wheel 24264 Feb 14 00:44 /bin/su

how i add the user to the group??

csfsmash · Post by **csfsmash** » Sat May 20, 2006 4:08 pm

ok i made this...

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userdel smash
adduser smash wheel

but now i dont have sound in X.. how i add the user to another group?? i mean to wheel and audio

gentoo_dude · Post by **gentoo_dude** » Sat May 20, 2006 4:17 pm

Check the log in /var/log/everything/current and see what is the error for the authentication. Probably pam has something to do with it.
To add a user to a group you do

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usermod -a -G <groupname> <username>

Or you can manually edit with your favorite editor the /etc/group file

roseZ · Post by **roseZ** » Sat May 20, 2006 4:42 pm

I think you should rather add user to a group with

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gpasswd -a <user> <group>

Did your su problem disappear, or did we just give you more grief?

gentoo_dude · Post by **gentoo_dude** » Sat May 20, 2006 5:04 pm

I think the problem was that the user was not in the wheel group. Since I found serveral posts on different forums specifying the on Gentoo and on some BSDs in order to run just "su" the user must be in the wheel group.

roseZ · Post by **roseZ** » Sat May 20, 2006 5:32 pm

gentoo_dude wrote:I think the problem was that the user was not in the wheel group.

It seems you are correct, although, as I tested it on my box the error message was different from csfsmash's. With user not in wheel I get this:

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$ su -
Password: 
su: Permission denied
Sorry.

It makes no difference whether I try to su root or any other user, which supports your assessment.

Edit:
OK, I did some checking. It indeed confirmed that user must be in wheel group to use su at all (this depends on system settings, though). It was csfsmash's error message that led me to suspect permission problems. Pretty thorough discussion on this whole su business can be found in this thread. I'd be glad if someone explained why /bin/sh was complaining about permissions.