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I accidentally renamed the directory /usr into /usr_bak.
I want to change it back, so I append the path /usr_bak/bin to $PATH to allow the system to find the command sudo.
But now sudo mv /usr_bak /usr gives me the error:
sudo: error while loading shared libraries: libsudo_util.so.0: cannot open shared object file: No such file or directory
Is there a way to rename the /usr_bak as /usr besides reinstalling the system?
Since you have set a password for root, use su and busybox, installed by default in Ubuntu. All of su's required libraries are in /lib. Busybox is a collection of utilities that's statically linked, so missing libraries shouldn't be a problem. Do:
su -c '/bin/busybox mv /usr_bak /usr'
(While Busybox itself also has a su applet, the /bin/busybox binary is not setuid and so doesn't work unless ran as root.)
If you don't have a root password, you could probably use Gilles' solution here using (Gilles says this won't work with setuid binaries like sudo) reboot and edit the GRUB menu to boot with LD_LIBRARY_PATH, orinit=/bin/busybox as a kernel parameter and move the folder back.
LD_LIBRARY_PATH wouldn't help to run sudo since sudo is setuid. If its libraries aren't in the right place, sudo won't work until root repairs it.
Mar 19, 2018 at 21:43
/sbin for precisely that kind of scenario: "I'm doing some activity where runtime libraries will be juggled around but need to still manipulate files." Basically the same approach before Busybox was invented. (The number of commands available in this fashion was very limited, because those statically linked binaries gobble up diskspace.)
/lib, then you'd probably have to reboot to init=/bin/busybox
In addition to muru's answer:
you could have used some rescue boot USB key to repair your system; e.g. if your system is some Debian or Ubuntu, boot the installation USB key in rescue mode, and do the appropriate mount and mv and umount.
to be able to repair more easily such mistakes, I generally also install a static shell with several builtin commands (notably with some cp, rm, mv-like builtins) such as sash (it is packaged in Debian & Ubuntu, and also available as sash-3.8.tar.gz in source form) and boot with init=/bin/sash passed to Grub.
PS: sash is slightly buggy, and not entirely Posix compliant, but still very useful.
apt-get install sash. But you could also download sash-3.8.tar.gz and compile it.
Mar 19, 2018 at 18:00
I think the best safest way is to reboot using a USB, CD or DVD booted OS (Debian, Ubuntu, Suse, etc). Then mount the drive containing the problems and do the rename.
Safer than booting into a minefield with /usr or /lib effectively missing.
I ran into a similar problem where I renamed /usr/bin to /usr/bin_bkp for some test and then I wasn't able to rename (as the command didn't find the sudo in the standard directory which is /usr/bin) and then I went to the /usr/bin_bkp directory manually (using File manager) and most of the functions (including the rename) on the right click are disabled.
Then I tried the following command and it fixed the issue
$/usr/bin_bkp/sudo mv /usr/bin_bkp/ /usr/bin/
I invoked the sudo from the current path and it worked, now everything's back to normal.
OS: Xubuntu 14.04
I can't try this right now (and am not sure I'd want to), but it seems like it ought to work to create yourself a new "/usr" as a hard link (not a soft link) to your "/usr_bak, then delete the "/usr_bak"
ln /usr_bak /usr
rm /usr_bak
The hard link created by "ln" (with no "-s" argument) in the file system should make both the usr and usr_bak directories equally valid links to the directories in question. "rm" just removes the one link you asked it to remove, not both of them. Since there's still a valid link to the contents, they should remain accessible through the remaining link at "/usr".
. and .., so the link count on a directory tells you the number of first-level subdirs). Also, rm doesn't work on directories, you'd have to use rmdir. (ln and rm work on symlinks to directories, but we're talking about an actual directory). Also, this doesn't solve the problem, because it requires root just like mv, because of the permissions on /. If you could run this, you could run mv instead like a normal person.
Mar 20, 2018 at 22:59
ln(1) on Debian says this for the the -d/-F/--directory option: "allow the superuser to attempt to hard link directories (note: will probably fail due to system restrictions, even for the superuser)". So you're free to try, but your filesystem probably won't let you.
Mar 21, 2018 at 10:35
sudoeven got to library stage, it's usually in/usr/bin/and should have failed with a command-not-found error. Also, do you have a root password set?not foundbefore so I appended the new path/usr_bak/binto$PATHand now I get the error in my post here.../usrof Ubuntu 16.04 to overwrite the/usrof Ubuntu 17.10...