System Administration

System administration covers the day-to-day tasks of maintaining a Linux system — managing disks, monitoring performance, reviewing logs, and securely connecting to remote servers. This lesson brings together the essential tools and practices.

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Disk Management

Viewing Disk Usage

df -h                            # show filesystem disk usage (human-readable)
df -h /                          # show usage for a specific mount point
du -sh /var/log                  # show total size of a directory
du -sh /home/*                   # show size of each user's home directory
du -h --max-depth=1 /var         # show size of immediate subdirectories

Block Devices

lsblk                            # list block devices (disks and partitions)
lsblk -f                         # include filesystem information
sudo fdisk -l                    # detailed partition information
blkid                            # show UUID and filesystem type

Example lsblk output:

NAME    MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda       8:0    0   100G  0 disk
├── sda1  8:1    0   512M  0 part /boot/efi
├── sda2  8:2    0    95G  0 part /
└── sda3  8:3    0   4.5G  0 part [SWAP]
sdb       8:16   0    50G  0 disk
└── sdb1  8:17   0    50G  0 part /data

Mounting and Unmounting

sudo mount /dev/sdb1 /mnt/data          # mount a partition
sudo umount /mnt/data                    # unmount
sudo mount -t ext4 /dev/sdb1 /mnt/data  # specify filesystem type

/etc/fstab — Persistent Mounts

# /etc/fstab
# <device>                                 <mount>    <type> <options>    <dump> <pass>
UUID=abcd-1234-5678                        /data      ext4   defaults     0      2
UUID=efgh-9012-3456                        /backup    xfs    defaults,noatime 0  2

sudo mount -a                    # mount all entries in /etc/fstab

Creating Filesystems

sudo mkfs.ext4 /dev/sdb1         # format as ext4
sudo mkfs.xfs /dev/sdb1          # format as XFS

Swap

free -h                           # show memory and swap usage
sudo swapon --show                # show active swap devices
sudo fallocate -l 4G /swapfile    # create a 4 GB swap file
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile
# Add to /etc/fstab for persistence:
# /swapfile none swap sw 0 0

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System Monitoring

System Information

uname -a                         # kernel version, architecture
hostnamectl                      # hostname and OS info
uptime                           # uptime and load average
lscpu                            # CPU information
free -h                          # memory and swap usage
cat /etc/os-release              # distribution information

Load Average

The load average shows how many processes are waiting for CPU over 1, 5, and 15 minutes:

$ uptime
 10:30:00 up 42 days,  3:15,  2 users,  load average: 0.50, 0.75, 1.20

Load Average	Interpretation (single-core)
0.0 – 0.7	Healthy
0.7 – 1.0	Starting to saturate
> 1.0	Overloaded (processes queuing)

Tip: For multi-core systems, divide the load by the number of CPU cores. A load of 4.0 on a 4-core system is equivalent to a load of 1.0 on a single core.

Performance Monitoring Tools

Tool	Purpose	Install
top / htop	Process monitoring	htop: sudo apt install htop
vmstat	Virtual memory statistics	Pre-installed
iostat	Disk I/O statistics	sudo apt install sysstat
sar	System Activity Reporter	sudo apt install sysstat
nmon	Comprehensive monitoring	sudo apt install nmon
dstat	Versatile resource statistics	sudo apt install dstat
iotop	I/O monitoring by process	sudo apt install iotop

vmstat 1 5                       # report every 1 second, 5 times
iostat -x 1                      # extended disk stats every second
sar -u 1 5                       # CPU usage every 1 second, 5 reports

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Log Management

Important Log Files