Exercise: Check /etc/fstab before you reboot

Check /etc/fstab before you reboot

• Verify an fstab file without rebooting.
• Use mount -a to test entries.
• Understand what nofail changes.

Start the exercise

On workstation, start the exercise. It removes a test mount from /etc/fstab if an earlier run left one.

[student@workstation ~]$ lab start sa-fstab

Later tasks assume that you are logged in to the server they name: ssh student@servera from workstation, then sudo -i for a root shell.

Back up and look

On servera as root, copy /etc/fstab to /root/fstab.bak and show its entries without comments.

[student@workstation ~]$ ssh student@servera
[student@servera ~]$ sudo -i
[root@servera ~]# cp /etc/fstab /root/fstab.bak
[root@servera ~]# grep -v '^#' /etc/fstab
LABEL=rootfs  /         ext4  defaults  0 0
LABEL=UEFI    /boot/efi vfat  defaults  0 0

Always keep a copy of a file you are about to break.

Add a mount that cannot work

Append a line mounting /dev/sdb1 on /data as xfs. The disk has no partition yet, and the directory /data does not exist. Run findmnt --verify and mount -a.

[root@servera ~]# echo '/dev/sdb1  /data  xfs  defaults  0 0' >> /etc/fstab
[root@servera ~]# findmnt --verify
/
   [W] recommended root FS passno is 1 (current is 0)
/data
   [E] unreachable on boot required target: No such file or directory
   [W] unreachable source: /dev/sdb1: No such file or directory
   [W] cannot detect on-disk filesystem type

0 parse errors, 1 error, 3 warnings
[root@servera ~]# mount -a
mount: /data: mount point does not exist.

The [E] is an error: the mount point is missing, and a line like this can stop the boot in emergency mode. You found it before rebooting. (The warnings about the source exist for the same reason, as the disk is not there.)

Create the mount point

Create /data and run both checks again. What changed, and what did not?

[root@servera ~]# mkdir /data
[root@servera ~]# findmnt --verify | tail -2

0 parse errors, 0 errors, 3 warnings
[root@servera ~]# mount -a; echo "status=$?"
mount: /data: special device /dev/sdb1 does not exist.
status=32

The error is gone, but mount -a still fails: the device does not exist. Without nofail, that failure would again be a problem at boot.

Add nofail

Change the line to use defaults,nofail. Run mount -a and look at its status.

[root@servera ~]# sed -i 's#^/dev/sdb1.*#/dev/sdb1  /data  xfs  defaults,nofail  0 0#' /etc/fstab
[root@servera ~]# mount -a; echo "status=$?"
status=0

nofail tells the system that this file system is optional: a missing device is skipped quietly, and the boot carries on. Use it for secondary disks, never for / or other essential file systems.

Restore the file

[root@servera ~]# cp /root/fstab.bak /etc/fstab
[root@servera ~]# systemctl daemon-reload
[root@servera ~]# findmnt --verify | tail -1
0 parse errors, 0 errors, 1 warning
[root@servera ~]# rm -f /root/fstab.bak
[root@servera ~]# rmdir /data
[root@servera ~]# exit
[student@servera ~]$ exit

Grade and finish

Check your work with lab grade sa-fstab, then put the exercise away with lab finish sa-fstab.