Verify the integrity and availability of resources

In this guide, you’ll learn how to monitor and verify the integrity of key resources on Linux servers. We cover disk and directory usage, memory and CPU statistics, file system repair (XFS and ext4), and service health checks.

Disk Space Usage

Over time, server storage fills up as applications grow and users store more data. Use df to inspect overall disk usage:

# Default: sizes in 1K blocks
df

For human-readable output (MB, GB, …), add the -h flag:

df -h
Filesystem                  Size  Used Avail Use% Mounted on
/dev/mapper/cs-root          17G  7.9G   9.2G  47% /
/dev/vda1                   1014M  435M  580M  43% /boot
tmpfs                       1.9G     0  1.9G   1% /dev/shm
...

Note

Ignore tmpfs entries—they represent in-memory filesystems, not physical disks.

Directory Usage

To measure the size of a specific directory, run du with summarization and human-readable flags:

du -sh /var/log
# e.g., 512M    /var/log

Warning

Running du on very large or deeply nested directories can take time and generate high I/O.

Memory Utilization

Display RAM and swap usage with free:

free -h
              total        used        free      shared  buff/cache   available
Mem:          3.6Gi       1.0Gi       1.5Gi        15Mi       1.1Gi       2.4Gi
Swap:         2.0Gi          0B       2.0Gi

Focus on the available column—it indicates memory ready for new applications.

CPU Load and Hardware Details

Load Averages

Use uptime to view load averages over 1, 5, and 15 minutes:

uptime
# 17:24:55 up 32 min,  1 user,  load average: 0.05, 0.05, 0.01

On a single-core system, load of 1.00 equates to 100% utilization.
On an 8-core system, a load of 6.00 means six cores were fully busy.

CPU Architecture

lscpu

Key fields:
• Architecture
• CPU(s)
• Thread(s) per core
• Model name
• Cache sizes

PCI Devices

lspci

Lists all PCI devices, including network adapters, GPUs, and host bridges.

File System Integrity

Repairing an XFS File System

Unmount the partition:
sudo umount /dev/vdb1
Repair with verbose output:
```
sudo xfs_repair -v /dev/vdb1
```
Remount after completion:
sudo mount /dev/vdb1 /mnt

Note

Always unmount the XFS volume before running xfs_repair to avoid data corruption.

Checking and Repairing an ext4 File System

Run fsck.ext4 with verbose, forced check, and preen (auto-fix simple issues):

sudo fsck.ext4 -v -f -p /dev/vdb2

-v: verbose output
-f: force check even if clean
-p: preen mode for unattended fixes

Warning

Do not run fsck on a mounted ext4 partition, especially the root (/), as it may cause data loss.

Monitoring Key Processes

List all service dependencies and their statuses with systemctl:

systemctl list-dependencies
# default.target
# ● └─accounts-daemon.service
# ● └─gdm.service
# ○ └─chronyd.service

● = running
○ = stopped

Example: simulate stopping NTP service, verify, then restart:

# Stop chronyd
sudo pkill chronyd

# Recheck dependencies
systemctl list-dependencies

# Inspect why it stopped
systemctl status chronyd.service

# Restart the service
sudo systemctl start chronyd.service

Command Summary

Command	Description	Key Flags
df	Show filesystem disk usage	-h (human readable)
du	Estimate directory space usage	-sh (summarize + human)
free	Display memory and swap usage	-h
uptime	Show system uptime and load averages	—
lscpu	Display CPU architecture and features	—
lspci	List PCI devices	—
xfs_repair	Repair XFS file systems	-v (verbose)
fsck.ext4	Check and repair ext4 partitions	-v, -f, -p
systemctl list-dependencies	List service dependencies and statuses	—