root locked out on CLI due to login shell problem

[st3623]

Hi all,

I'm out of ideas on how to regain root SSH access to my DS1511+ after an upgrade to DSM 4.0 and a subsequent attempt to reinstall ipkg.

Here is what happened:
- Under DSM 3.2 I had installed a number of ipkg packages, one of them being zsh. Unfortunately (now I know better) I have changed the root login shell to `/opt/bin/zsh` without creating a backup user with id 0.
- After the upgrade to DSM 4.0 I wanted to reinstall all my ipkg stuff from scratch and cleared out everything in /opt.
- I logged out.

Current status:
- I can't (SSH) login as root anymore, SSH always errors out with `/opt/bin/zsh: No such file or directory`.
- I can ssh in with the `admin` account, but since it doesn't have write access to most parts of the filesystem it's not of much use (still, I have read access to almost everything).
- The rest of the system is running nicely.

What I tried so far:
- ssh in as `admin` and `su <something>`: doesn't work since busybox cannot run su from a non-root account.
- `ssh root@host /bin/ash` doesn't work, since SSH still errors out with `/opt/bin/zsh: No such file or directory`.
- `scp fixedfile root@host:/etc/passwd` also fails with the same error.

Questions:
- Is there some known way to use the DSM web interface to fix `/etc/passwd` ?
- If there is no way to regain root SSH access without reinstalling the system, how do I best go about it with minimal reconfiguration effort and, of course, without loosing the contents of my data disks?

I'm seriously looking forward to any help on this...

Cheers,
Mathias

[maxxfi]

Try to force a reinstallation of DSM 4.0 (or try 4.1 beta ).
It should reset the /etc/passwd

[st3623]

Ok, problem fixed.

The solution was to use a custom .pat "firmware update" file.
Even though more than 4 years old the info [on this page]http://oinkzwurgl.org/diskstation_patchfiles is still current, it works nicely even for DSM 4.0.

What I did:
- download the syno-universal-pat_20080227.tar.gz template
- add one line to file "updater2": sed -i -e "s/opt\/bin\/zsh/bin\/ash/" /etc/passwd
- repackage into a .pat file
- upload and run via the web interface

The script runs through nicely, as the root user.
So, if anybody should shut themselves out: with a custom .pat file you can do pretty much anything.

Cheers,
Mathias

[CoolRaoul]

It's a bad and risky idea to change root default shell

One alternative (and IMHO safer) solution would be to add the following code at the beginning of root's profile (/root/.profile), providing the same results without any potential damage

Code: Select all

if [ "$ZSH_VERSION" = "" ] ;then
    case $- in
        # only for interactive shells
        # (just to be safe but not really needed)
        *i*)
            echo >&2 "exec'ing zsh"
            exec zsh --login
            ;;
    esac
fi


[maxxfi]

I fully agree with previous solution, but before the "exec zsh --login", I would suggest also to test if zsh is present.
I used to believe that 'exec' is able to verify it itself, but it seems to me that the Synology/busybox version doesn't perform any checks.

[CoolRaoul]

before the "exec zsh --login", I would suggest also to test if zsh is present

Right,
To do this, simply replace 1st line with:

Code: Select all

if [ "$ZSH_VERSION" = "" ] && which zsh >/dev/null 2>&1 ; then

[norrellmeister]

I had this exact problem. Managed to fix it by installing a package called "config file editor", through the web UI, and using that to edit /etc/passwd. Another thing to keep in mind is that, if you have it set up, you may be able to fix this by editing /etc/passwd through SCP.