Resizing Filesystems with LVM - CentOS 7

See how much space is available on physical disk:

[root@centos ~]# pvs
  PV         VG    Fmt  Attr PSize   PFree
  /dev/sda2  volg0 lvm2 a--  199.00g 21.00g

See what sizes your logical volumes are:
[root@centos ~]# lvs
  LV   VG    Attr       LSize  Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  home volg0 -wi-ao---- 16.00g
  opt  volg0 -wi-ao---- 32.00g
  root volg0 -wi-ao---- 32.00g
  swap volg0 -wi-ao---- 66.00g
  var  volg0 -wi-ao---- 32.00g

See what size your filesystems are:

[root@centos ~]# df -h
Filesystem              Size  Used Avail Use% Mounted on
/dev/mapper/volg0-root   32G  1.2G   29G   4% /
devtmpfs                 32G     0   32G   0% /dev
tmpfs                    32G     0   32G   0% /dev/shm
tmpfs                    32G  9.0M   32G   1% /run
tmpfs                    32G     0   32G   0% /sys/fs/cgroup
/dev/sda1               976M  129M  796M  14% /boot
/dev/mapper/volg0-home   16G   45M   15G   1% /home
/dev/mapper/volg0-var    32G  172M   30G   1% /var
/dev/mapper/volg0-opt    32G   49M   30G   1% /opt
tmpfs                   6.3G     0  6.3G   0% /run/user/0

Resize your logical volume - in this case /var adding 10G to current 32G = 42G:

[root@centos ~]# lvresize -L 42G /dev/mapper/volg0-var
  Size of logical volume volg0/var changed from 32.00 GiB (8192 extents) to 42.00 GiB (10752 extents).
  Logical volume var successfully resized.

Underlining volume is expanded, but not filesystem on top:

[root@centos ~]# df -h
Filesystem              Size  Used Avail Use% Mounted on
/dev/mapper/volg0-root   32G  1.2G   29G   4% /
devtmpfs                 32G     0   32G   0% /dev
tmpfs                    32G     0   32G   0% /dev/shm
tmpfs                    32G  9.0M   32G   1% /run
tmpfs                    32G     0   32G   0% /sys/fs/cgroup
/dev/sda1               976M  129M  796M  14% /boot
/dev/mapper/volg0-home   16G   45M   15G   1% /home
/dev/mapper/volg0-var    32G  172M   30G   1% /var
/dev/mapper/volg0-opt    32G   49M   30G   1% /opt
tmpfs                   6.3G     0  6.3G   0% /run/user/0

So resize filesystem on top:

[root@centos ~]# resize2fs /dev/mapper/volg0-var
resize2fs 1.42.9 (28-Dec-2013)
Filesystem at /dev/mapper/volg0-var is mounted on /var; on-line resizing required
old_desc_blocks = 4, new_desc_blocks = 6
The filesystem on /dev/mapper/volg0-var is now 11010048 blocks long.

See now filesystem is 42GB in size:

[root@centos ~]# df -h
Filesystem              Size  Used Avail Use% Mounted on
/dev/mapper/volg0-root   32G  1.2G   29G   4% /
devtmpfs                 32G     0   32G   0% /dev
tmpfs                    32G     0   32G   0% /dev/shm
tmpfs                    32G  9.0M   32G   1% /run
tmpfs                    32G     0   32G   0% /sys/fs/cgroup
/dev/sda1               976M  129M  796M  14% /boot
/dev/mapper/volg0-home   16G   45M   15G   1% /home
/dev/mapper/volg0-var    42G  172M   40G   1% /var
/dev/mapper/volg0-opt    32G   49M   30G   1% /opt
tmpfs                   6.3G     0  6.3G   0% /run/user/0

Job done:

[root@centos ~]#