System Config

All system configuration in Shanios follows standard Linux conventions — edit files in /etc, manage services with systemctl. Your changes are captured by the OverlayFS upper layer and survive every OS update and rollback.

How the /etc Overlay Works

Lower layer (read-only): /etc from the active @blue or @green slot
Upper layer (writable):  /data/overlay/etc/upper/
Merged view:             /etc (what you see and interact with)

When you write to any /etc file, the kernel copies it from the lower layer to the upper layer and applies your change. When the OS updates (new lower layer), your upper-layer files are untouched. Files you have never modified automatically reflect the new OS defaults.

Editing /etc Files

Nothing special is required — edit files in /etc exactly as on any Linux system:

sudo nano /etc/hostname
sudo nano /etc/hosts
sudo nano /etc/locale.conf
sudo nano /etc/environment
sudo nano /etc/ssh/sshd_config
sudo nano /etc/fstab

# Edit systemd service overrides
sudo systemctl edit sshd.service           # creates a drop-in override
sudo systemctl edit --full sshd.service    # full copy you can modify freely

Changes take effect immediately (or after service restart for daemon config) and survive every OS update.

Viewing Your Customisations

# Every /etc file you have modified
find /data/overlay/etc/upper/ -type f | sort

# Compare a modified file to the OS default
diff /data/overlay/etc/upper/ssh/sshd_config \
     /etc/ssh/sshd_config

Reverting a File to OS Default

# Remove the upper-layer version — the OS default becomes active again
sudo rm /data/overlay/etc/upper/ssh/sshd_config

Resetting All /etc Customisations

Use shani-reset rather than raw rm -rf to avoid leaving the overlay work directory in an inconsistent state:

# Factory reset all persistent system state in /data (keeps /home and OS slots intact)
sudo shani-reset

# Preview what would be wiped without making changes
sudo shani-reset --dry-run

# Keep previously downloaded OS images
sudo shani-reset --keep-downloads

Locale & Timezone

sudo localectl set-locale LANG=en_IN.UTF-8
sudo localectl set-keymap us
sudo localectl set-x11-keymap us
sudo timedatectl set-timezone Asia/Kolkata

localectl status
timedatectl status

Hostname

sudo hostnamectl set-hostname my-machine
hostnamectl

Your machine is reachable as hostname.local on the local network via Avahi (mDNS), active by default.

Managing Services

# Enable/disable a service (persists across reboots via overlay)
sudo systemctl enable --now sshd
sudo systemctl disable sshd

# Start/stop/restart
sudo systemctl start sshd
sudo systemctl stop sshd
sudo systemctl restart sshd
sudo systemctl reload nginx

systemctl status sshd
journalctl -u sshd -f
journalctl -u sshd --since today

systemctl list-unit-files --state=enabled
systemctl --failed

User Services

systemctl --user enable --now my-service.service
systemctl --user status my-service.service
journalctl --user -u my-service.service -f

User service unit files live in ~/.config/systemd/user/.

Adding Custom systemd Units

sudo nano /etc/systemd/system/myapp.service
sudo systemctl daemon-reload
sudo systemctl enable --now myapp.service

Units placed in /etc/systemd/system/ are captured by the overlay and persist across updates.

sysctl Tuning

# Temporary (lost on reboot)
sudo sysctl vm.swappiness=10

# Persistent
echo "vm.swappiness=10" | sudo tee /etc/sysctl.d/99-custom.conf
sudo sysctl --system   # apply without reboot

Common customisations:

# /etc/sysctl.d/99-custom.conf
vm.swappiness=10
fs.inotify.max_user_watches=524288
fs.file-max=2097152

Kernel Parameters

Permanent kernel parameter changes are embedded in the UKI via gen-efi, not via /etc/default/grub. The generated command line is written to /etc/kernel/install_cmdline_<slot> on each run and cannot be manually pre-edited (it is overwritten). To add a permanent parameter, contact the project or use a dracut.conf.d snippet — then rebuild:

sudo gen-efi configure blue   # rebuild UKI for the currently booted slot

See gen-efi Reference for details.

Network Configuration

NetworkManager handles all network configuration. Wi-Fi passwords, VPN profiles, and static IP configurations persist in /data/varlib/NetworkManager across all updates and rollbacks.

nmcli connection show
nmcli device wifi connect "SSID" password "password"
nmcli device status

Time Synchronisation

systemd-timesyncd is enabled by default:

sudo nano /etc/systemd/timesyncd.conf
# [Time]
# NTP=time.cloudflare.com
# FallbackNTP=pool.ntp.org

sudo systemctl restart systemd-timesyncd
timedatectl timesync-status

PAM & sudo

sudo visudo

# Add a sudoers drop-in (safer than editing /etc/sudoers directly)
sudo nano /etc/sudoers.d/my-rules
# username ALL=(ALL) NOPASSWD: /usr/bin/specific-command