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A colleague of mine told me that after he executed the below command, he's not able to login to the system.

  • No user can login via ssh.

  • Only normal users can login over physical console of the system, but no administrative commands are allowed, not even

    # sudo su -

And the culprit command which did the damage was

# chmod -R 777 /

My question, of course is, how to deal with such a system? Is there a way to restore the default permissions on a Linux system and what's best way to handle such situations?

G-Man Says 'Reinstate Monica'
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Sollosa
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    "what's best way to handle such situations?" [Captain's Mast](https://en.wikipedia.org/wiki/Mast_(naval)) and a yard-arm. Fixes that problem every single time. – Warren Young Apr 29 '16 at 04:16
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    short answer: unfixable. but here's a dirty hack that can partially do the job on debian systems http://unix.stackexchange.com/a/49978/7696 - if you use a different unix or distro you may be able to adapt some of the ideas. or it's probably easier/better to just backup your data & config files and re-install from scratch. – cas Apr 29 '16 at 05:09
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    BTW, ssh is disallowed because the `chmod -R 777` messed up the perms of all `.ssh` directories (including root's) and the files in them. `ssh` is **very** fussy about perms. If you want to login via ssh in order to attempt fixing this, the first thing you need to do is fix the home dir perms (`/home/user/` and `/root/`) and the `~/.ssh/` perms. Also the perms for `/` and `/home`. – cas Apr 29 '16 at 05:13
  • Can you restore from backups? – Mark Plotnick Apr 29 '16 at 08:42
  • @cas thanks, I really understand the consequences of the command. Not to surprise you, It was new thing for me. I tried it on a machine as well, luckily was virtual, but faced same situation. – Sollosa Apr 29 '16 at 11:12
  • @cas there is are backup files, but I'm not sure which folders to be replaced. Is there a way that we could sync the permissions of one system with the affected one? – Sollosa Apr 29 '16 at 11:14
  • @MarkPlotnick thanks Mark! there are backup files, but I'm not sure which folders to be replaced. Is there a way that we could sync the permissions of one system with the affected one? – Sollosa Apr 29 '16 at 11:15
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    If you can restore the backups to a new filesystem, and mount both the correct and incorrect filesystems on the same computer, you can use `find` to walk through the file tree and run a bunch of `chmod` commands, using the `--reference` option of `chmod` to copy the permissions. I'll see if there's an example online. – Mark Plotnick Apr 29 '16 at 11:32
  • @MarkPlotnick that's much better I think, but do I have to replace every folder one by one or can you suggest a command that would hold reference to all files and folders on newlyinstalled system to apply on the oldsystem? I mean it would be nice, and thanks again Mark! – Sollosa Apr 29 '16 at 11:36
  • @Sollosa I once saw a shell script here (can't find it atm) that would scan a file tree (that had the correct permissions) and produce a shell script containing chmod commands to fix up a similar tree that had incorrect permissions. – Mark Plotnick Apr 29 '16 at 14:25
  • @MarkPlotnick that would be helpful though, thanks anyhow – Sollosa Apr 30 '16 at 19:20
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    Found it on serverfault. The answers there should fix things up: [Copy permissions to identical tree on linux / unix](http://serverfault.com/questions/58277/copy-permissions-to-identical-tree-on-linux-unix) – Mark Plotnick Apr 30 '16 at 20:57

1 Answers1

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If you can't login or su to a root user, the two remaining options are

  1. Boot from rescue media, and repair the damage
  2. Boot from installer, reinstall the system, then restore data from backups
Michael Mrozek
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Toby Speight
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