Maintenance

Routine maintenance tasks for both systems, including garbage collection, store optimisation, SSD maintenance, and monitoring.

Garbage Collection

Laptop

Managed automatically by nh:

programs.nh.clean = {
  enable = true;
  dates = "weekly";
  extraArgs = "--keep-since 3d --keep 3";
};

• Runs weekly as a systemd timer
• Removes generations older than 3 days
• Always keeps at least 3 generations

Manual GC:

# Dry run to see what would be removed
nix store gc --dry-run

# Actually collect garbage
nix store gc

Server

nix.gc = {
  automatic = true;
  dates = "weekly";
  options = "--delete-older-than 7d";
};

• Runs weekly
• Removes all generations older than 7 days
• No minimum generation count (the server should always be on the latest)

Store Optimisation

Both systems enable automatic store optimisation:

nix.optimise = {
  automatic = true;
  dates = [ "weekly" ];
};

nix.settings.auto-optimise-store = true;

Setting	Effect
nix.optimise.automatic	Runs nix store optimise weekly (deduplicates store paths via hardlinks)
auto-optimise-store	Optimises new paths as they're added to the store

Both are enabled for belt-and-suspenders deduplication. The weekly job catches any paths that were added without optimisation.

SSD Maintenance (fstrim)

Both systems enable weekly TRIM:

services.fstrim = {
  enable = true;
  interval = "weekly";
};

This runs fstrim -av weekly, which informs the SSD firmware about unused blocks, maintaining write performance and extending drive lifespan.

Server I/O Schedulers

The server sets I/O schedulers per device type via udev rules:

services.udev.extraRules = ''
  # HDD
  ACTION == "add|change", KERNEL=="sd[a-z]*", ATTR{queue/rotational}=="1", \
    ATTR{queue/scheduler}="bfq"

  # SSD
  ACTION=="add|change", KERNEL=="sd[a-z]*|mmcblk[0-9]*", ATTR{queue/rotational}=="0", \
    ATTR{queue/scheduler}="mq-deadline"

  # NVMe SSD
  ACTION=="add|change", KERNEL=="nvme[0-9]*", ATTR{queue/rotational}=="0", \
    ATTR{queue/scheduler}="none"
'';

Device Type	Scheduler	Rationale
HDD (rotational)	bfq	Budget Fair Queuing; optimises for latency with rotating media
SATA SSD	mq-deadline	Simple deadline scheduler; good for SATA SSDs with limited parallelism
NVMe SSD	none	NVMe handles its own queuing; any software scheduler adds overhead

Systemd Timers Overview

All automated maintenance tasks are systemd timers. To see the full schedule:

systemctl list-timers --all

Server Timers

Timer	Schedule	Service
nixos-upgrade.timer	Weekly	System auto-upgrade
restic-backups-backup.timer	Daily	Restic backup
nix-gc.timer	Weekly	Nix garbage collection
nix-optimise.timer	Weekly	Nix store optimisation
fstrim.timer	Weekly	SSD TRIM

Laptop Timers

Timer	Schedule	Service
nh-clean.timer	Weekly	Generation cleanup
nix-optimise.timer	Weekly	Nix store optimisation
fstrim.timer	Weekly	SSD TRIM

Disk Usage Monitoring

# Check overall disk usage
df -h

# Check Nix store size
du -sh /nix/store

# Check number of store paths
ls /nix/store | wc -l

# Check Restic repository size (server)
du -sh /backup

# Check persistent data size (server)
du -sh /persist/*

Server-Specific Maintenance

Impermanence Cleanup

Old root subvolumes are automatically cleaned up during the boot rollback script. Subvolumes older than 30 days are deleted:

for i in $(find /btrfs_tmp/old_roots/ -maxdepth 1 -mtime +30); do
    delete_subvolume_recursively "$i"
done

No manual intervention needed.

Container Health

# List running containers
machinectl list

# Check a specific container's status
machinectl status traefik

# View container logs
journalctl -M traefik -f

# Restart a container
sudo machinectl restart traefik

Checking for Failed Services

# List all failed units
systemctl --failed

# On the server, also check inside containers
for c in traefik authelia adguard immich vaultwarden opencloud; do
  echo "=== $c ==="
  machinectl shell $c /run/current-system/sw/bin/systemctl --failed
done

Minimal Server Packages

The server intentionally ships very few packages to minimise attack surface:

environment.systemPackages = with pkgs; [
  btop    # System monitor
  yazi    # File manager
  helix   # Text editor
  lynis   # Security auditor
  agenix  # Secrets management CLI
];

Documentation, fonts, XDG, man pages, and the dynamic linker stub are all disabled. See Server Overview for the full list of disabled features.