Top Linux Commands for Disk Space Monitoring
by Maxime Decooman
Monitoring disk space on Linux servers is a critical aspect of system administration. Running out of disk space can cause application failures, prevent logging, and even crash your system. Here are a few commands to help you.
1. Display Free Disk Space
The most commonly used command for checking disk space. This command shows each mounted filesystem, its total size, used space, available space, usage percentage, and mount point. Regular monitoring helps prevent disk space emergencies.
df -h
# The -h flag displays sizes in human-readable format (KB, MB, GB)
# Result example:
Filesystem Size Used Avail Use% Mounted on
tmpfs 97M 1.1M 96M 2% /run
/dev/vda1 24G 8.8G 15G 38% /
tmpfs 481M 1.1M 480M 1% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
/dev/vda16 881M 112M 707M 14% /boot
/dev/vda15 105M 6.1M 99M 6% /boot/efi
tmpfs 97M 12K 97M 1% /run/user/1000
2. Display Filesystem Types
Add the parameter -T to get the filesystem type. Different filesystem types (ext4, xfs, btrfs, etc.) have different features and limitations regarding maximum file sizes, total capacity, and performance characteristics.
df -hT
# Result example:
Filesystem Type Size Used Avail Use% Mounted on
tmpfs tmpfs 97M 1.1M 96M 2% /run
/dev/vda1 ext4 24G 8.8G 15G 38% /
tmpfs tmpfs 481M 1.1M 480M 1% /dev/shm
tmpfs tmpfs 5.0M 0 5.0M 0% /run/lock
/dev/vda16 ext4 881M 112M 707M 14% /boot
/dev/vda15 vfat 105M 6.1M 99M 6% /boot/efi
tmpfs tmpfs 97M 12K 97M 1% /run/user/1000
3. Check Inode Usage
Each file on a Linux system uses an inode (index node), which stores metadata about the file. An inode exhaustion can prevent new file creation even with available disk space. Monitoring inode usage is critical for systems that handle numerous small files, such as mail or web servers.
df -i
# Result example
Filesystem Inodes IUsed IFree IUse% Mounted on
tmpfs 123085 784 122301 1% /run
/dev/vda1 3145728 210820 2934908 7% /
tmpfs 123085 3 123082 1% /dev/shm
tmpfs 123085 3 123082 1% /run/lock
/dev/vda16 58496 604 57892 2% /boot
/dev/vda15 0 0 0 - /boot/efi
tmpfs 24617 32 24585 1% /run/user/1000
4. Check Size of a Directory
The disk usage (du) command with -s (summarize) and -h (human-readable) flags displays the total size of a specified directory and its contents.
du -sh /var/log
# Result
1.2G /var/log
This command is invaluable for quickly identifying which directories are consuming significant space. Use it to target potential cleanup locations when space is running low.
5. Display Directory Sizes
A more granular alternative to -sh is to show the size of all immediate subdirectories without recursing deeper into the directory tree. This helps identify which top-level directories are consuming the most space. You may need to use sudo to have the read permissions.
sudo du -h --max-depth=1 /var
# The --max-depth=1 parameter is particularly useful for exploring space
# usage hierarchically without being overwhelmed by thousands of files.
# Result
4.0K /var/mail
40M /var/spool
4.0K /var/local
1.3G /var/log
...
2.7G /var
6. Sort Directories by Size
Pipe the sort for sorting to display directories ordered by size (largest first), making it easier to identify space hogs.
sudo du -h --max-depth=1 /var | sort -hr
# -h parameter compares according to human readable numbers.
# -r parameter means reverse (biggest to smallest).
# Result
1.3G /var
1.2G /var/log
132M /var/cache
12M /var/backups
24K /var/tmp
4.0K /var/mail
7. Interactive Disk Usage Analyzer
A more user-friendly, interactive version of du with a text-based interface. It allows navigation through directories and provides a visual representation of space usage.
ncdu /var
ncdu provides key-based navigation to browse directories, delete files, and quickly identify space-consuming directories.
# Result example
--- /var -----------------------------------------------------
. 1.3 GiB [##################] /log
. 577.7 MiB [####### ] /lib
. 336.3 MiB [#### ] /cache
2.9 MiB [ ] /backups
. 420.0 KiB [ ] /spool
52.0 KiB [ ] /snap
8. Find Large Files
Uses the find command to search the entire filesystem for files larger than 100MB. This targeted approach helps identify specific large files that might be candidates for deletion or archiving.
find / -type f -size +100M
# Adjust the size parameter (+100M) as needed.
# Add `-exec ls -lh {} \;` to see detailed file information
# including human-readable sizes.
# Result
/var/log/journal/7aa9dd79e9e94f0f9519591df3024c5a/system.journal
/home/user/Downloads/large-file.iso
9. List Files Sorted by Size
Lists files in the current directory, sorted by size (largest first) with human-readable sizes. This provides a quick snapshot of the largest files in a specific directory.
ls -laSh
# The parameters used are:
# -l (long format),
# -a (all files including hidden),
# -S (sort by size), and
# -h (human-readable sizes).
# Result example:
total 1.2G
-rw-r--r-- 1 user user 500M Apr 10 12:34 database.dump
-rw-r--r-- 1 user user 350M Apr 9 09:12 backup.tar.gz
-rw-r--r-- 1 user user 120M Apr 8 22:45 logs.tar
10. List Block Devices
This command provides an overview of your storage devices and their organization. It helps identify all available storage, including unmounted devices, which is useful for storage planning and troubleshooting.
lsblk
# Result example:
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 500G 0 disk
├─sda1 8:1 0 30G 0 part /
├─sda2 8:2 0 434G 0 part /home
└─sda3 8:3 0 36G 0 part [SWAP]
sdb 8:16 0 1T 0 disk
└─sdb1 8:17 0 1T 0 part /data
11. List Disk Partitions
This low-level tool shows the exact layout of partitions on the disk, which is helpful for disk management, troubleshooting, and planning partition changes. It requires root privileges.
sudo fdisk -l
# Result example:
Disk /dev/sda: 500 GiB
Device Boot Start End Sectors Size Id Type
/dev/sda1 * 2048 62914559 62912512 30G 83 Linux
/dev/sda2 62914560 973078527 910163968 434G 83 Linux
/dev/sda3 973078528 1048575999 75497472 36G 82 Linux swap
12. Monitor Disk I/O
Displays real-time disk I/O statistics for processes, similar to how top shows CPU usage. This helps identify which processes are causing heavy disk activity.
sudo iotop
# Result example:
Total DISK READ: 0.00 B/s | Total DISK WRITE: 0.00 B/s
Current DISK READ: 0.00 B/s | Current DISK WRITE: 0.00 B/s
PID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND
1 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % systemd --system
1234 be/4 user 0.00 B/s 1.12 M/s 0.00 % 0.12 % python backup.py
13. Display Mounted Filesystems
This command provides a comprehensive view of all mount points in your system, which helps in understanding the filesystem hierarchy and diagnosing mount-related issues.
findmnt
# Result example:
TARGET SOURCE FSTYPE OPTIONS
/ /dev/sda1 ext4 rw,relatime
├─/sys sysfs sysfs rw,nosuid,nodev,noexec
│ ├─/sys/kernel/security securityfs securityfs rw,nosuid,nodev,noexec
│ ├─/sys/fs/cgroup tmpfs tmpfs ro,nosuid,nodev,noexec
...
├─/home /dev/sda2 ext4 rw,relatime
14. Logical Volume Management
These commands are essential for managing LVM (Logical Volume Management)-based storage, which provides flexibility for resizing filesystems and managing storage across multiple physical disks. Many enterprise systems use LVM for storage management.
sudo pvs
# Result example:
PV VG Fmt Attr PSize PFree
/dev/sda3 vg_sys lvm2 a-- 100.00g 10.00g
sudo vgs
# Result example:
VG #PV #LV #SN Attr VSize VFree
vg_sys 1 2 0 wz--n- 100.00g 10.00g
sudo lvs
# Result example:
LV VG Attr LSize Pool Origin Data% Meta%
lv_root vg_sys -wi-ao---- 50.00g
lv_home vg_sys -wi-ao---- 40.00g
15. Check Disk Usage by File Type
The find command combined with du can help identify space usage by specific file types, which is useful for targeted cleanup operations.
sudo find /path/to/search -name "*.log" -type f -exec du -ch {} \+ | grep total$
# This example finds all .log files and shows their total size
# You can replace "*.log" with any file extension (.zip, .mp4, etc.)
# Result example:
450M total
An article will follow to build a monitoring dashboard based on some of these commands.