Written 6 Sep 2026. This is a how-to, not a product card.

When the old PC feels slow

SSH lags, apt crawls, or the house share feels sticky. Check load, memory, disk room, then one busy job. Skip a new mini PC tonight.

Only the house folder crawls while SSH feels fine? That is usually the network or the stick, not this whole-box walk: when the house share is slow. Fan screams but commands still snappy? Start with when the old PC's fan is loud. This note is the computer itself feeling heavy: typing in SSH hesitates, packages crawl, or everything on the box is sluggish together.

Skip until the box is reachable

If SSH never connects, fix that first: when SSH won't connect. Soft-off or a dead screen is is it still on? or when the old PC won't boot. A Wi-Fi radio that keeps falling off feels like "slow" until you check the link: when house Wi-Fi on the old PC keeps dropping. You need a working SSH session (or a keyboard on the computer) for the checks below.

What this is

An old OptiPlex or laptop left on for Pi-hole and a share can feel fine for weeks, then one job eats the CPU, memory fills, or the system disk packs full of logs and photos. You read four numbers (load, free memory, disk room, one busy process), match the story, and fix that one thing. You don't buy a new N100 because apt and a local chat model were fighting for the same 8 GB.

Step 1: load and uptime

On the computer:

uptime

The three load numbers are 1, 5, and 15 minutes. On a dual-core office box, sustained load around 2 or higher means the cores are busy. Fresh reboot with load near 0 that climbs only when you copy photos is a different story than load stuck above the core count all day.

Also:

uptime -p

If it has been awake for weeks and weekly updates already ran, check whether a reboot is waiting: see if a reboot is needed. A pending reboot after a kernel update can leave odd lag until you restart once at a quiet time.

Step 2: memory

free -h

Look at the available column (or available under Mem). A few hundred MB available on an 8 GB box, with swap climbing, is a memory squeeze. Total installed size is a separate look: see how much memory the computer already has. Free room right now: see if the computer still has free memory. Overflow on disk: see if the computer already has extra memory on disk.

If you started a local chat model on this same PC, that is a common memory hog: run a local chat on the old PC. Stop the model when you are not using it, or keep chat on a second box. Pi-hole alone is light. A big model on 8 GB is not.

Step 3: disk room

df -h /

If the root filesystem is at 95% or shows 100%, everything feels slow: logs, apt, Samba, even SSH can stutter. Confirm it is the system disk (not the backup stick), then free room or move the house folder: when the computer's disk is full. Inodes (many tiny files) can fill while df -h still looks fine — that walk covers the inode check too.

Step 4: who is busy

Snapshot once:

ps aux --sort=-%cpu | head -n 12

Or the interactive view:

top

Press q to quit. Find one line eating CPU or memory: a stuck apt / dpkg, a runaway sync, a model server, a browser you left open on a desktop install. The short drill for reading that list is see what is keeping the computer busy.

Weekly updates stuck or locking the package tools: when weekly updates won't install. You usually wait out the other updater or finish an interrupted dpkg — not a new CPU.

Step 5: heat and dust (if load is high and the case is hot)

Put a hand near the vents. Hot case plus high load and a loud fan is air and dust, not a shopping list: when the old PC's fan is loud, and don't bury the vents: don't cook the computer. Thermal throttle feels exactly like "the box got slow after it warmed up."

Step 6: disk health if it stays slow with low load

Load near idle, memory free, disk not full, but every file open still crawls? A dying drive does that. Quick SMART check before you trust photos: see if the old disk is dying. Back up the house folder first if SMART looks ugly: a backup of the house folder.

What this is not

This is not a new mini PC, more RAM soldered on a board that cannot take it, or a 10G switch for a sluggish SSH session. It is not the share-only slow walk (Wi-Fi vs cable to the laptop). It is not opening the computer to the public internet so a cloud monitor can graph load. It is not blaming Pi-hole for CPU when a chat model or a full disk is the real story.

What next

Memory was the bottleneck? Re-check after you stop the heavy job: see if the computer still has free memory. Disk was packed: when the computer's disk is full. Fan and heat: when the old PC's fan is loud. Only the share crawls: when the house share is slow. Pending kernel reboot: see if a reboot is needed.

Optional: jot what was busy (apt, model, disk %) in Lab plan — username + passkey, no email. Skip if you just want to keep reading.

Skip

• Skip a new N100 or soldered-RAM upgrade before you read load, free memory, and df once.
• Skip blaming Pi-hole for CPU until you see it at the top of ps or top.
• Skip a 10G switch or a new mesh kit for a sluggish SSH session on the computer itself.
• Skip leaving a big local chat model running all day on an 8 GB box you also use for the share.
• Skip this if SSH never connects — fix the connect walk first.
• Skip this if only phone photo copies crawl and SSH is snappy — use the share-slow walk.