03.Dynamic expansion of directories under Linux, taking allocating part of home space to root as an example

Introduction
1. Allocation details
2. Uninstall home
3. Expand root
4. Rebuild /home

Introduction

This article will introduce how to allocate part of the home directory to the root directory under Linux.
General idea: Uninstall home, release its disk capacity occupation -> expand root, increase its disk space -> rebuild and restore home
The operation demonstration environment is CentOS system, and other operating systems such as openEuler can also be used as a reference.

The operating system version is as follows

name	Version
CentOS	7.6+

1. Allocation details

Executing the lsblk command, you can see that
centos-home has allocated more storage space, while root only has 50G. If there is
no additional disk space to continue to allocate (if there is, please refer to: 01. Directory expansion under Linux to increase the size of the root directory Taking disk capacity allocation as an example )
, you need to free up part of the home space and allocate it to root (in actual application scenarios, root usage is relatively large after all)

[root@localhost harbor]# lsblk
NAME            MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sr0              11:0    1  66.7M  0 rom  /mnt
vda             252:0    0     1T  0 disk
├─vda1          252:1    0     1G  0 part /boot
└─vda2          252:2    0  1023G  0 part
  ├─centos-root 253:0    0    50G  0 lvm  /
  ├─centos-swap 253:1    0  31.5G  0 lvm  [SWAP]
  └─centos-home 253:2    0 941.5G  0 lvm  /home
[root@localhost harbor]#

2. Uninstall home

2.1 Terminate the process

Kill all processes under the /home file system (Note: Do not execute fuser -km home in the /home directory）

Execution error: -bash: fuser: command not found.
Problem analysis: When minimizing the installation of centos, there is no fuser command, resulting in the inability to fence.
Solution: yum install psmisc

[root@localhost portainer]# cd ~
[root@localhost ~]# fuser -km home

2.2 Backup /home

[root@localhost ~]# tar cvf /run/home.tar /home
tar: 从成员名中删除开头的“/”
/home/
/home/harbor/
/home/harbor/harbor.v2.8.2.tar.gz

2.3 Uninstall /home

[root@localhost ~]# umount /home
[root@localhost ~]#

2.4 Delete the logical volume lv where /home is located

Tip: Logical volume centos/home contains a filesystem in use
Solution: Remount mount /home and execute 2.1 to terminate the process (or other methods to terminate the process under the /home file system)

[root@localhost ~]# lvremove /dev/mapper/centos-home
Do you really want to remove active logical volume centos/home? [y/n]: y
  Logical volume "home" successfully removed
[root@localhost ~]#

3. Expand root

3.1 Expand the logical volume lv where /root is located

After uninstalling home, about 950G will be left vacant.
Here, 800G will be allocated to root.

[root@localhost ~]# lvextend -L +800G /dev/mapper/centos-root
  Size of logical volume centos/root changed from 50.00 GiB (12800 extents) to 850.00 GiB (217600 extents).
  Logical volume centos/root successfully resized.
[root@localhost ~]#

3.2 Expand the /root file system

[root@localhost ~]# xfs_growfs /dev/mapper/centos-root
meta-data=/dev/mapper/centos-root isize=512    agcount=4, agsize=3276800 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0 spinodes=0
data     =                       bsize=4096   blocks=13107200, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal               bsize=4096   blocks=6400, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
data blocks changed from 13107200 to 222822400
[root@localhost ~]#

3.3 Check whether the expansion is successful

You can see that centos-root has been successfully expanded to 1023G

[root@localhost ~]# lsblk
NAME            MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sr0              11:0    1 66.7M  0 rom  /mnt
vda             252:0    0    1T  0 disk
├─vda1          252:1    0    1G  0 part /boot
└─vda2          252:2    0 1023G  0 part
  ├─centos-root 253:0    0  850G  0 lvm  /
  └─centos-swap 253:1    0 31.5G  0 lvm  [SWAP]
[root@localhost ~]#

4. Rebuild /home

4.1 Create the logical volume lv where /home is located

[root@localhost ~]# lvcreate -L 141G -n /dev/mapper/centos-home
  Logical volume "home" created.
[root@localhost ~]#

4.2 Create the /home file system

[root@localhost ~]# mkfs.xfs  /dev/mapper/centos-home
meta-data=/dev/mapper/centos-home isize=512    agcount=4, agsize=9240576 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
data     =                       bsize=4096   blocks=36962304, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=18048, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
[root@localhost ~]#

4.3 Mount the newly created file system to the /home directory

[root@localhost ~]# mount /dev/mapper/centos-home
[root@localhost ~]#

4.4 Restore /home contents

Remember to restore stopped programs under home

[root@localhost ~]# tar xvf /run/home.tar -C /
home/
home/harbor/
home/harbor/harbor.v2.8.2.tar.gz

4.5 Delete backup

[root@localhost ~]# rm -rf /run/home.tar
[root@localhost ~]#