/tmp: Read-only file system Error

If you are getting the error "Read-only file system" while editing some files on the server, you can fix the same by running File System Check. 

Error example:

$ crontab -e
/tmp/crontab.XXXX1ibTLU: Read-only file system

It shows that the /tmp partition is unwriteable. The read-only has been mounted as read-only because file-system facing some error. To fix this, we need to do file system check (fsck) for /tmp partition. Before we do fsck, we need to unmount the directory but following error occurred:

$ umount /tmp
/tmp: Device or resource busy

It seems like /tmp directory is locked to be unmounted due to some files are already in process/being opened/being executed by some other processes. Using lsof, we can list out all the open files:

$ lsof | grep /tmp
mysqld  2599 mysql    5u   REG    7,0    0 6098 /tmp/ibaqFhew (deleted)
mysqld  2599 mysql    6u   REG    7,0    0 6099 /tmp/ibC7Yfbn (deleted)
mysqld  2599 mysql    7u   REG    7,0    0 6100 /tmp/ibJ8AFbe (deleted)
mysqld  2599 mysql   11u   REG    7,0    0 6101 /tmp/ibrLO9t5 (deleted)

As we can see that mysqld is locking some temporary files in /tmp directory. The 2nd column shows PID of the locking process. We need to stop this process using kill command:

$ kill -9 2599

Only then we are able to unmount the /tmp:

$ umount /tmp

Make sure that there is no error being prompt during the unmounting process. Now we can proceed to do fsck with -f (force) and -y (always accept prompt as Yes) to automate the file system check process:

$ fsck -f -y /tmp
fsck 1.39 (29-May-2006)
e2fsck 1.39 (29-May-2006)
/usr/tmpDSK: recovering journal
Pass 1: Checking inodes, blocks, and sizes
Deleted inode 6097 has zero dtime.  Fix? yes

Inodes that were part of a corrupted orphan linked list found.  Fix? yes

.

.

/usr/tmpDSK: ***** FILE SYSTEM WAS MODIFIED *****
/usr/tmpDSK: 316/128016 files (3.2% non-contiguous), 66394/512000 blocks

Now the file system has been modified and fixed. We can remount back the partition using following command:

$ mount -a

You should able to use back the /tmp partition at this time.