how to find string boot on the /etc/fstab file and replace UUID with kernel device name /dev/sda1?

Question

cat /etc/fstab
/dev/mapper/vg00-root   /                       xfs     defaults        0 0
UUID=6fc6605f-796e-4e0b-a8f7-8b339c46b1a9 /boot                   xfs     defaults        0 0
/dev/mapper/vg00-tmp    /tmp                    xfs     defaults        0 0
/dev/mapper/vg00-var    /var                    xfs     defaults        0 0
/dev/mapper/vg00-crash  /var/crash              xfs     defaults        0 0
/dev/mapper/vg00-log    /var/log                xfs     defaults        0 0
/dev/mapper/vg00-swap   swap                    swap    defaults        0 0

sed 's/UUID/\/dev\/sda1/g' /etc/fstab

So, what does not work? See https://ideone.com/4YqrQm, your code replaces `UUID` with `/dev/sda1` — Wiktor Stribiżew, Oct 22 '19 at 09:36
@WiktorStribiżew probably OP is looking to change UUID only if line contains `boot`... `how to find string boot on the /etc/fstab file and replace UUID` — Sundeep, Oct 22 '19 at 09:40
Then, maybe `sed '/\/boot/{s,UUID,/dev/sda1,}' /etc/fstab`, see https://ideone.com/oMmtUb — Wiktor Stribiżew, Oct 22 '19 at 09:42
see also https://stackoverflow.com/questions/5864146/using-different-delimiters-in-sed-commands-and-range-addresses to avoid using `\/` — Sundeep, Oct 22 '19 at 09:42
Aha, so you want to replace the whole `UUID=6fc6605f-796e-4e0b-a8f7-8b339c46b1a9` with a new value. Or not? You accepted an answer that does not check for `/boot` — Wiktor Stribiżew, Oct 22 '19 at 09:50
@SuhasiniSubramaniam adding complete expected output for given sample would avoid such confusion.. please do so for future questions — Sundeep, Oct 22 '19 at 09:52
@WiktorStribiżew You are right and below answer helped. sed '/\/boot/{s,UUID[^ ]*,/dev/sda1,}' /etc/fstab — Suhasini Subramaniam, Oct 22 '19 at 10:16
What you ask for does not correlate with the accepted solution, hence, I suggest closing the question as unclear. — Wiktor Stribiżew, Oct 22 '19 at 10:37

score 0 · Answer 1 · answered Oct 22 '19 at 09:40

List files under /dev/disk/by-uuid:

ls -l /dev/disk/by-uuid/

...to obtain something like this:

lrwxrwxrwx 1 root root 10 ott  4 18:37 53bc3708-e45d-4352-977a-a62c6a4fd5c8 -> ../../dm-1
lrwxrwxrwx 1 root root 10 ott  4 18:37 6a23dfcf-e36d-45c8-a468-d3976b5239f3 -> ../../dm-0
lrwxrwxrwx 1 root root 10 ott  4 18:37 7d6e75e9-7ed2-4412-8acd-2de50ffa0034 -> ../../sda1

As you see, you find the old style device name in the right of the output, as link target.

In the uplevel directory, you can find disks categorized by id and by path, not only by uuid. Beautiful!

score 0 · Accepted Answer · answered Oct 22 '19 at 09:40

I'm making the assumption that you want to replace UUID=6fc6605f-796e-4e0b-a8f7-8b339c46b1a9 for /dev/sda1/, which is in general a bad idea. The UUID is a unique id belonging to the disk. If you want to replace the disk, I suggest to try to get the UUID with blkid.

Otherwise, you should extend the regex in order to replace that part:

$ sed 's/UUID=6fc[^ ]*/\/dev\/sda1/g' fstab

Note that U've added 6fc to make sure you will not change every UUID= line.

how to find string boot on the /etc/fstab file and replace UUID with kernel device name /dev/sda1?

2 Answers2