Do you hate how Centos 7 defaults to allocating most of your valuable space to /home even though it is a production server?

Here is a quick guide on how to take back that space live, while online (of course make sure you have backups just in case something goes wrong!):

First we will reduce our home dir by 100G:

lvreduce -L -100G /dev/mapper/centos-home
  WARNING: Reducing active and open logical volume to <5.12 GiB.
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce centos/home? [y/n]: y
  Size of logical volume centos/home changed from <105.12 GiB (26910 extents) to <5.12 GiB (1310 extents).
  Logical volume centos/home successfully resized.
 

Now let's give it back to /root:

lvextend -l 100%FREE /dev/centos/root
  Size of logical volume centos/root changed from 50.00 GiB (12800 extents) to 100.00 GiB (25601 extents).
  Logical volume centos/root successfully resized.

OK but now what does our filesystem magically know what we did with the LV/logical volume?  No


[root@disc livefilesystem]# df -h
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/centos-root   50G   35G   16G  70% /
devtmpfs                 1.9G     0  1.9G   0% /dev
tmpfs                    1.9G     0  1.9G   0% /dev/shm
tmpfs                    1.9G  8.7M  1.9G   1% /run
tmpfs                    1.9G     0  1.9G   0% /sys/fs/cgroup
/dev/mapper/centos-home  106G   33M  106G   1% /home
/dev/sda1               1014M  176M  839M  18% /boot
tmpfs                    379M     0  379M   0% /run/user/0

Maybe we could just remount it? No

[root@disc livefilesystem]# mount -o remount /
[root@disc livefilesystem]# df -h
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/centos-root   50G   35G   16G  70% /


How do we resize the filesystem?  xfs_growfs of course!

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 26215424

Now it's all good!

[root@disc livefilesystem]# df -h
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/centos-root  100G   35G   66G  35% /
devtmpfs                 1.9G     0  1.9G   0% /dev
tmpfs                    1.9G     0  1.9G   0% /dev/shm
tmpfs                    1.9G  8.7M  1.9G   1% /run
tmpfs                    1.9G     0  1.9G   0% /sys/fs/cgroup
/dev/mapper/centos-home  106G   33M  106G   1% /home
/dev/sda1               1014M  176M  839M  18% /boot
tmpfs                    379M     0  379M   0% /run/user/0


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