How to Shrink /home and Expand Root Partition on a Linux Log Server

1. Problem Description

The log server was originally set up with an unreasonable partition layout, leaving the /home partition oversized and the root partition lacking space.

2. Goal

Reduce the size of the /home partition, extend the root ( /) partition, and ensure the system boots correctly after the changes.

3. Unmounting /home

Attempting to unmount /home fails with “target busy”. The usual way to find which process is using the mount point is with fuser -m /home or lsof, but the fuser command is missing.

# umount /home
umount: /home：目标忙。

4. Installing fuser

On CentOS/RHEL 7 the fuser utility is provided by the psmisc package.

# yum install psmisc

5. Identifying and Killing the Process

After installing fuser, run it to locate the offending process and terminate it.

# fuser -m /home   // continue to find who uses /home
# kill -9 11757    // stop the process
# umount /home    // unmount /home filesystem

6. Shrinking the /home Partition

Resize the logical volume to the desired size (e.g., 100 GB) using resize2fs for ext4 filesystems.

# resize2fs -p /dev/mapper/centos-home 100G

7. Verifying Filesystem Type

Check /etc/fstab to confirm the filesystem type of centos-home. If it is XFS, additional tools are required for expansion.

# cat /etc/fstab | grep centos-home

8. Installing XFS Tools (if needed)

For XFS expansion, install the xfsdump utility.

# yum install xfsdump -y

9. Expanding the Root Partition

After reducing /home to 100 GB, the freed space can be allocated to the root logical volume, extending the / directory.

10. Remounting /home

Attempt to mount /home again. If the mount fails with a superblock error, the partition must be formatted again, so back up all data before shrinking.

# mount /home
mount: /dev/mapper/centos-home：不能读超级块

Therefore, before reducing the size of /home, ensure a complete backup of its contents.

11. Final Steps

Re‑mount the /home partition after the root expansion and verify that both partitions are functional.