4. System Administration

systemd Deep Dive

systemd is Arch’s init system and service manager. Virtually all Arch-based distros use it.

Core Commands

# Start/stop/restart services
systemctl start <service>
systemctl stop <service>
systemctl restart <service>
 
# Enable/disable at boot
systemctl enable <service>
systemctl disable <service>
 
# Check status
systemctl status <service>
 
# List running services
systemctl list-units --type=service
systemctl list-units --state=running
 
# View dependency tree
systemctl list-dependencies <service>
 
# Show failed units
systemctl --failed

Unit Files

Located in /usr/lib/systemd/system/ (packages) and /etc/systemd/system/ (local overrides).

Service unit example (/etc/systemd/system/myservice.service):

[Unit]
Description=My Application
After=network.target
 
[Service]
Type=simple
ExecStart=/usr/bin/myapp --foreground
ExecReload=/bin/kill -HUP $MAINPID
Restart=on-failure
RestartSec=5s
User=myapp
 
[Install]
WantedBy=multi-user.target

Timer unit (cron replacement):

[Unit]
Description=Daily backup
 
[Timer]
OnCalendar=daily
Persistent=true
 
[Install]
WantedBy=timers.target

Targets (Runlevels)

Target	Purpose
`poweroff.target`	System halt
`rescue.target`	Single user mode
`multi-user.target`	CLI multi-user
`graphical.target`	GUI multi-user
`reboot.target`	Reboot

# Change default target
systemctl set-default multi-user.target
 
# Switch target temporarily
systemctl isolate multi-user.target

Managing Boot Process

# View boot time
systemd-analyze
systemd-analyze blame     # By time consumed
 
# View service logs
journalctl -u <service>
journalctl -f             # Follow logs
journalctl --since "1 hour ago"
 
# Clean old journal entries
journalctl --vacuum-time=2weeks
journalctl --vacuum-size=500M

Boot Process

Arch’s boot sequence:

UEFI/BIOS → loads Boot Loader
Boot Loader (systemd-boot/GRUB) → loads kernel + initramfs
initramfs (early userspace) → detects hardware, opens LUKS, mounts root
systemd → starts all units per target

initramfs (mkinitcpio)

Regenerated after kernel upgrades or config changes.

# Generate new initramfs
mkinitcpio -P
 
# Config: /etc/mkinitcpio.conf
# HOOKS order matters:
HOOKS=(base udev autodetect keyboard keymap encrypt lvm2 resume filesystems)
 
# Common hooks:
# base       — minimum tools
# udev       — device enumeration
# autodetect — skip unnecessary modules
# keyboard   — keyboard support
# encrypt    — LUKS support
# lvm2       — LVM support
# resume     — Hibernation support
# filesystems — fsck, mounting

Kernel Arguments

# View current
cat /proc/cmdline
 
# Add to GRUB: /etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash mitigations=off"
 
# Add to systemd-boot: /boot/loader/entries/arch.conf
options root=UUID=<uuid> rw mitigations=off
 
# Apply GRUB changes
grub-mkconfig -o /boot/grub/grub.cfg

Kernel Management

Installing Kernels

# Official kernels
pacman -S linux           # Current (default)
pacman -S linux-lts       # Long-term support
pacman -S linux-zen        # Optimized (zen scheduler)
 
# Install extra kernel
pacman -S linux61         # Kernel 6.1.x
 
# Manjaro-specific
mhwd-kernel -i linux61    # Manjaro's kernel manager
 
# Remove kernel
pacman -R linux

Updating Kernel

# Upgrade includes kernel
pacman -Syu
 
# Manually regenerate initramfs after kernel change
mkinitcpio -P

Kernel Modules

# List loaded modules
lsmod
 
# Load module manually
modprobe <module>
 
# Block module from loading (e.g., nouveau)
# /etc/modprobe.d/blacklist.conf
blacklist nouveau
 
# Module parameters
# /etc/modprobe.d/params.conf
options <module> param=value

System Maintenance

Regular Maintenance Tasks

# Full system upgrade
pacman -Syu
 
# After upgrade (check for .pacnew files)
pacdiff
 
# Clean package cache
paccache -r              # Keep last 1 version
# Or in /etc/pacman.conf:
CleanMethod = KeepCurrent
 
# Remove orphans
pacman -Rns $(pacman -Qdtq)
 
# Check for filesystem errors
fsck /dev/sda1
 
# Repair filesystem
fsck -fy /dev/sda1       # Force repair

pacman Config

# /etc/pacman.conf
 
[options]
# Parallel downloads
ParallelDownloads = 5
 
# Color output
Color
 
# Verbose package lists
VerbosePackageLists
 
# Clean cache on upgrade
CleanMethod = KeepCurrent
 
# Hold packages (don't upgrade)
HoldPkg = pacman glibc
 
# Ignore group changes
IgnoreGroup = base
 
# Skip file from upgrade
NoUpgrade = etc/pacman.conf

mkinitcpio (Initramfs Generation)

Key hooks:

Hook	Purpose
`base`	Core utilities
`udev`	Dynamic device loading
`autodetect`	Skip unused modules
`keyboard`	Keyboard support (for LUKS at boot)
`keymap`	Load keymap
`encrypt`	LUKS decryption
`lvm2`	LVM activation
`resume`	Hibernation resume
`filesystems`	Root mount
`fsck`	Filesystem check

# Generate with custom preset
mkinitcpio -P
 
# Kernel-specific
mkinitcpio -k /boot/vmlinuz-linux -P
 
# Show what changed
mkinitcpio -L

Systemd-journald (Logging)

# View logs
journalctl -b              # Current boot
journalctl -e              # End (latest)
journalctl -f              # Follow
journalctl -u <service>    # Specific service
journalctl --since "2024-01-01" --until "2024-01-02"
 
# Priority levels
journalctl -p err          # Errors and worse
 
# Disk usage
journalctl --disk-usage
journalctl --vacuum-time=2weeks
journalctl --vacuum-bytes=500M
 
# Persistent logs across boots
# /etc/systemd/journald.conf
[Journal]
Storage=persistent

Package Hooks (Automatic Actions)

Triggered on package install/upgrade/remove.

# /etc/pacman.d/hooks/update-grub.hook
[Trigger]
Type = Package
Operation = Install
Operation = Upgrade
Target = grub
 
[Action]
Description = Regenerating GRUB config...
When = PostTransaction
Exec = /usr/bin/grub-mkconfig -o /boot/grub/grub.cfg
 
# Another example: update initramfs on kernel install
[Trigger]
Type = Package
Operation = Install
Target = linux
 
[Action]
Description = Regenerating initramfs...
When = PostTransaction
Exec = /usr/bin/mkinitcpio -P

Systemd Slice & Resource Control

# Create slice for a service
# /etc/systemd/system/myapp.slice
[Slice]
CPUWeight=50
MemoryMax=512M
 
# In service unit:
[Service]
Slice=myapp.slice

cron-equivalent: systemd Timers

# Daily timer example
[Unit]
Description=Daily cleanup
 
[Timer]
OnCalendar=daily
Persistent=true
 
[Install]
WantedBy=timers.target
 
# Timer paired with service
systemctl enable --now mytimer.timer
systemctl list-timers

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