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mr.zog
Asked: 2019-04-27 09:17:55 +0800 CST

How do I resize a logical volume to the size of the filesystem within it?

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Target system is CentOS 6.x but resizing operations will be done in %pre section of CentOS 7.6 kickstart.

I have already run resize2fs -M /dev/mapper/centos-home successfully. If I mount the volume, df says it's 100% full. This is good.

Now I need to reduce the size of the logical volume to match the size of the ext4 filesystem. I don't want to use rough estimates. I also don't need to conserve every possible extent. Within a >= 1GB range is fine. i.e. volume can be reduced to 1GB >= filesystem size.

The target volume does contain data I can't lose. I don't have shell (or any other) access to the system. The system has no CentOS repos available so I cannot upgrade it. I don't even have remote hands I can talk to. I'm using a different computer to build and test my install ISO on.

My %pre syntax/script needs to safely reduce /dev/mapper/centos-home so I can create a new root volume for CentOS 7.6 install. Yes, this entire proposition is nuts.

centos7

2 Answers

  1. Best Answer

    Do it in one step.

    /sbin/lvresize --resizefs --size -8g  /dev/mapper/centos-home

    Where 8g is the size of the root volume you want to install.

    Constant size may be acceptable because the size of your new install is predictable.

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  2. It's not really a script per se.

    rootvol=/dev/mapper/vg_stt-lv_root
mkdir /tmp/rootlv
mount -t ext4 -o ro $rootvol /tmp/rootlv
usedROOT=$(df -h $rootvol |  tail -1 | awk '{print $2}' | awk '{printf("%d\n",$1 + 1)}')
umount /tmp/rootvol
/sbin/lvresize --resizefs --size $usedROOT\g  $rootvol
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