Help with UUID replacement in fstab and menu.lst

Shell Programming and Scripting
1

I am trying to write a small backup application for Linux systems file by file if partitions are created by the user using fdisk. I am facing a problem when I am done with restoring the files. The problem is with UUID mismatch in restored fstab and menu.lst.

Using C I could create a partlist.txt file where I have 3 entries:
device_name, "UUID" mountpoint

Need to restore the following:

  1. UUID in menu.lst by matching UUID of "/" from partlist.txt
  2. Replace correct UUIDs from partlist.txt for all mountpoints in fstab

Also cannot depend on the ordering of lines anywhere.

Attached the sample generated partlist.txt and fstab + menu.lst from Red Hat 6.
I am not an expert in using sed and awk. So any help is really appreciated.

2

Something like this..

miro@miro-ntb:Downloads$ cat partlist.txt 
/dev/sda1 "f75b104c-678e-4f80-a618-70d4bf4a3ede" /
/dev/sda3 "hsjsd675-678e-4f80-a618-70d4bf4a3ede" /home
/dev/sda2 "psb8767c-678e-4f80-a618-70d4bf4a3ede" /boot

miro@miro-ntb:Downloads$ cat fstab.txt 
#
# /etc/fstab
# Created by anaconda on Mon Feb 14 16:03:26 2011
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
/dev/mapper/VolGroup-lv_root /                       ext4    defaults        1 1
UUID=10cb97f9-e52e-472b-a20b-c1e90c6d561b /boot                   ext4    defaults        1 2
/dev/mapper/VolGroup-lv_swap swap                    swap    defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0
HHH     /home  smthn defs 0 0 

miro@miro-ntb:Downloads$ awk '
NR==FNR{a[$3]=$2; next} #store uuids in assoc. array
{ #on each line from fstab
for(i in a) { #loop through array
  if($2==i)  #check whether mountpoint is the same
  {$1="UUID=" a} #replace 1st field with UUID=uuid
}; 
print $0;  #print the whole line
}
' <(sed -e 's/\r//' -e 's/"//g' partlist.txt) fstab.txt  

#
# /etc/fstab
# Created by anaconda on Mon Feb 14 16:03:26 2011
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=f75b104c-678e-4f80-a618-70d4bf4a3ede / ext4 defaults 1 1
UUID=psb8767c-678e-4f80-a618-70d4bf4a3ede /boot ext4 defaults 1 2
/dev/mapper/VolGroup-lv_swap swap                    swap    defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0
UUID=hsjsd675-678e-4f80-a618-70d4bf4a3ede /home smthn defs 0 0

The sed command gets rid of carriage return and quotes.

3

Hi mirni,

Thank you so much. I have tried this just now and it works like a charm for the /etc/fstab file.

I need to replace the same in menu.lst file also (attached as menu.txt). Would you please provide the script for that also?

4

This is the script to modify menu.txt. It modifies the file in-place. It'd be safer to omit sed's '-i' switch in the second line, and let it print out the new version of menu.txt (redirect it into a new file); so that the original is kept untouched.

miro@miro-ntb:Downloads$ cat test.sh
#!/bin/bash

root_uuid=$(sed -n ' s/[^ ]* "// ;/\/[\r]*$/  s/".*//p' partlist.txt) #extract root UUID
sed -i 's/root=[^ ]*/root=UUID='$root_uuid'/' menu.txt #this file will get modified

miro@miro-ntb:Downloads$ cat menu.txt 
# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE:  You have a /boot partition.  This means that
#          all kernel and initrd paths are relative to /boot/, eg.
#          root (hd0,0)
#          kernel /vmlinuz-version ro root=/dev/mapper/VolGroup-lv_root
#          initrd /initrd-[generic-]version.img
#boot=/dev/sda
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Red Hat Enterprise Linux (2.6.32-71.el6.i686)
    root (hd0,0)
    kernel /vmlinuz-2.6.32-71.el6.i686 ro root=/dev/mapper/VolGroup-lv_root rd_LVM_LV=VolGroup/lv_root rd_LVM_LV=VolGroup/lv_swap rd_NO_LUKS rd_NO_MD rd_NO_DM LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=us crashkernel=auto rhgb quiet
    initrd /initramfs-2.6.32-71.el6.i686.img
miro@miro-ntb:Downloads$ ./test.sh
miro@miro-ntb:Downloads$ cat menu.txt 
# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE:  You have a /boot partition.  This means that
#          all kernel and initrd paths are relative to /boot/, eg.
#          root (hd0,0)
#          kernel /vmlinuz-version ro root=UUID=f75b104c-678e-4f80-a618-70d4bf4a3ede
#          initrd /initrd-[generic-]version.img
#boot=/dev/sda
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Red Hat Enterprise Linux (2.6.32-71.el6.i686)
    root (hd0,0)
    kernel /vmlinuz-2.6.32-71.el6.i686 ro root=UUID=f75b104c-678e-4f80-a618-70d4bf4a3ede rd_LVM_LV=VolGroup/lv_root rd_LVM_LV=VolGroup/lv_swap rd_NO_LUKS rd_NO_MD rd_NO_DM LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYBOARDTYPE=pc KEYTABLE=us crashkernel=auto rhgb quiet
    initrd /initramfs-2.6.32-71.el6.i686.img
5

Thanks a lot mirni!

---------- Post updated at 06:15 PM ---------- Previous update was at 06:08 PM ----------

One question mirni...
Is there any way to edit fstab in-place too? Otherwise I need to redirect the lines in a temp file and replace fstab again.

6

AFAIK awk doesn't support in-place editing. A workaround is needed. If anyone knows how to deal with this with the original "awk < (sed file1) file2" design, please post.

miro@miro-ntb:Downloads$ cat fstab.txt 

#
# /etc/fstab
# Created by anaconda on Mon Feb 14 16:03:26 2011
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
/dev/mapper/VolGroup-lv_root /                       ext4    defaults        1 1
UUID=10cb97f9-e52e-472b-a20b-c1e90c6d561b /boot                   ext4    defaults        1 2
/dev/mapper/VolGroup-lv_swap swap                    swap    defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0
miro@miro-ntb:Downloads$ { rm fstab.txt && awk '
BEGIN{while ( (getline < "partlist.txt")>0) { 
gsub(/\r|"/,""); a[$3]=$2;}
}
{
for(i in a) { if($2==i){$1="UUID=" a}}; 
print $0;
}' > fstab.txt; } < fstab.txt
miro@miro-ntb:Downloads$ cat fstab.txt 

#
# /etc/fstab
# Created by anaconda on Mon Feb 14 16:03:26 2011
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=f75b104c-678e-4f80-a618-70d4bf4a3ede / ext4 defaults 1 1
UUID=psb8767c-678e-4f80-a618-70d4bf4a3ede /boot ext4 defaults 1 2
/dev/mapper/VolGroup-lv_swap swap                    swap    defaults        0 0
tmpfs                   /dev/shm                tmpfs   defaults        0 0
devpts                  /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                   /sys                    sysfs   defaults        0 0
proc                    /proc                   proc    defaults        0 0

This workaround is adapted from here: sed / awk - inplace or inline edit. You can find an explanation how this '{ rm file && awk > file ; } < file' construct works.
Cheers
mirni

7

Thanks really!