MongoDB crashed because /var/log hit 100% capacity. Instead of just truncating logs (temporary fix), I extended the filesystem permanently.

# Check filesystem type
df -T /var/log
Filesystem                    Type  Size  Used Avail Use% Mounted on
/dev/mapper/rootvg-var_loglv  xfs   2.0G  2.0G   20K 100% /var/log

# Check available space in volume group
vgs
VG     #PV #LV #SN Attr   VSize   VFree
rootvg   1  10   0 wz--n- 100.00g 10.00g

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

# Grow XFS filesystem (online, no downtime!)
xfs_growfs /var/log

# Verify the expansion
df -h /var/log
Filesystem                     Size  Used Avail Use% Mounted on
/dev/mapper/rootvg-var_loglv  4.0G  1.3G  2.8G  32% /var/log

Key points:

  • xfs_growfs works on mounted filesystem (no downtime)
  • For ext4, use resize2fs instead
  • Always check VG free space with vgs before extending

Pro tip: Use lsblk -f to see all filesystems and their types at once.