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I am using Ubuntu 11.04.

I mistyped and wrote sudo chmod 444 / instead of writing /home.

Everything went blank and icons started disappearing, and now when I try to run Ubuntu, it hangs on the initial Ubuntu sign.

I know that I have changed the permissions for root itself, but is there any way I can revert back?

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up vote 5 down vote accepted

If you've only chmod'ed you root directory:

In linux, use chmod 755 to restore correct root directory access rights.

In Mac OS X, the sticky bit must be set, too. Use chmod +t / if you've already corrected the rights to 755. If not, you can do both at once using chmod 1755 /.

For both systems: Don't forget sudo if necessary.

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Thanks a lot :) Entered this in the root prompt and everything got recovered .... – user57162 Oct 25 '11 at 19:24
Did chmod / once for educational reasons and took me quite some while to figure out the sticky but stuff. :) – Jens Erat Oct 25 '11 at 19:27
-1, / is not supposed to have the sticky bit set. It's only for /tmp. – grawity Oct 25 '11 at 19:43
@grawity Looks you're right, it isn't set on my linux boxes either. You need it on OS X machines, I misconcieved this would be the same in linux. Will edit my answer. – Jens Erat Oct 25 '11 at 19:55
@grawity: it's because OS X allows the admin group write access to /, and without the sticky bit an admin could do nasty things like rename & replace top-level dirs without needing to go through any special authentication (sudo or the like). – Gordon Davisson Oct 25 '11 at 23:00

You may be able to boot into single user mode/rescue mode at the initial grub bootloader
If that doesn't work you can use an ubuntu or other boot disk such as Knoppix to boot your system, mount the / fs and correct it.
This is assume you did chmod 444 / not chmod -R 444 /

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Good call on the recursion switch... let's hope you're right. – andyortlieb Oct 25 '11 at 19:14
how do i boot in the rescue mode ? And yes i did did the first one not the second – user57162 Oct 25 '11 at 19:14
Can you still get to a shell at all? Do you still have one open? – andyortlieb Oct 25 '11 at 19:17
Okayz things have changed ... went into recovery mode and then clicked on drop to root shell prompt ... Can you tell me what should i now enter to correct everything ? – user57162 Oct 25 '11 at 19:19
root is normally 755, so if you can do chmod 755 / that should restore it to a normal state – freedenizen Oct 25 '11 at 19:30

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