Resize Filesystem Without Reboot

1. Toggle some informations about the root filesystem:

df /
# Filesystem     1K-blocks     Used Available Use% Mounted on
# /dev/vda3       71412992 58923184   9039732  87% /

2. /dev/vda3 is the second partition of block device /dev/vda. To size up this partition, you can use the tool parted.

parted /dev/vda resizepart 3 100%
# Warning: Partition /dev/sda2 is being used. Are you sure you want to continue?
# Yes/No? yes
# Information: You may need to update /etc/fstab.

3. After changing size of partition, you have to size up the filsystem too:

resize2fs /dev/vda3
# resize2fs 1.45.5 (07-Jan-2020)
# Filesystem at /dev/vda3 is mounted on /; on-line resizing required
# old_desc_blocks = 4, new_desc_blocks = 9
# The filesystem on /dev/vda3 is now 18019403 (4k) blocks long.

4. This is for checking modifications:

df /
# Filesystem     1K-blocks    Used Available Use% Mounted on
# /dev/vda3       70817420 5253016  62349464   8% /