> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Verify the integrity and availability of resources
> This guide teaches monitoring and verifying the integrity of key resources on Linux servers, including disk usage, memory, CPU statistics, and service health checks.
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:
```bash theme={null}
# Default: sizes in 1K blocks
df
```
For human-readable output (MB, GB, …), add the `-h` flag:
```bash theme={null}
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
...
```
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:
```bash theme={null}
du -sh /var/log
# e.g., 512M /var/log
```
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`:
```bash theme={null}
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:
```bash theme={null}
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
```bash theme={null}
lscpu
```
Key fields:\
• Architecture\
• CPU(s)\
• Thread(s) per core\
• Model name\
• Cache sizes
### PCI Devices
```bash theme={null}
lspci
```
Lists all PCI devices, including network adapters, GPUs, and host bridges.
## File System Integrity
### Repairing an XFS File System
1. **Unmount** the partition:\
`sudo umount /dev/vdb1`
2. **Repair** with verbose output:
```bash theme={null}
sudo xfs_repair -v /dev/vdb1
```
3. **Remount** after completion:\
`sudo mount /dev/vdb1 /mnt`
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):
```bash theme={null}
sudo fsck.ext4 -v -f -p /dev/vdb2
```
* `-v`: verbose output
* `-f`: force check even if clean
* `-p`: preen mode for unattended fixes
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`:
```bash theme={null}
systemctl list-dependencies
# default.target
# ● └─accounts-daemon.service
# ● └─gdm.service
# ○ └─chronyd.service
```
* `●` = running
* `○` = stopped
Example: simulate stopping NTP service, verify, then restart:
```bash theme={null}
# 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 | — |
## Links and References
* [df(1) Manual Page](https://man7.org/linux/man-pages/man1/df.1.html)
* [du(1) Manual Page](https://man7.org/linux/man-pages/man1/du.1.html)
* [free(1) Manual Page](https://man7.org/linux/man-pages/man1/free.1.html)
* [xfs\_repair(8) Manual Page](https://man7.org/linux/man-pages/man8/xfs_repair.8.html)
* [fsck.ext4(8) Manual Page](https://man7.org/linux/man-pages/man8/fsck.ext4.8.html)
* [systemctl(1) Manual Page](https://man7.org/linux/man-pages/man1/systemctl.1.html)