After the MongoDB disk-full incident, I decided to permanently expand /var/log instead of just truncating logs.

The server used XFS filesystem on LVM. Discovered I could expand it while mounted - no downtime needed!

# Check filesystem type
df -T /var/log
Filesystem                    Type  Size  Used
/dev/mapper/rootvg-var_loglv  xfs   2.0G  1.8G

# Check available space in volume group
vgs
VG     VSize   VFree
rootvg 100.00g 10.00g  # Have 10G free

# Extend the logical volume
lvextend -L +2G /dev/mapper/rootvg-var_loglv

# Grow the XFS filesystem (WHILE MOUNTED!)
xfs_growfs /var/log

# Verify
df -h /var/log
Filesystem                     Size  Used
/dev/mapper/rootvg-var_loglv  4.0G  1.8G

Key points:

  • xfs_growfs works on mounted filesystems (no unmount needed)
  • For ext4, use resize2fs instead
  • Always check vgs first to ensure free space exists
  • The command: xfs_growfs /mount/point (NOT the device path)

Expanded the filesystem during business hours, zero downtime. MongoDB kept running the whole time.

For ext4 filesystems, same process but different resize command:

lvextend -L +2G /dev/mapper/rootvg-var_loglv
resize2fs /dev/mapper/rootvg-var_loglv