Written 29 Aug 2026. This is a how-to, not a product card. Buy links are not tagged yet.

Make a leftover-box file runnable

After SSH works, change leftover-box file permissions with chmod so a practice script can run. You do not need a permissions GUI for this.

Put a short line into a leftover-box file parks words on disk. See what's in a leftover-box folder can show the permission letters. Tonight you only need those letters to mean “this file may run.” chmod changes who can read, write, or run a leftover-box file. You are still only practicing in home. The leftover box does not need a desktop, a permissions GUI, or a NAS for this one job.

Skip until SSH already works

SSH from the couch should already get you a leftover-box prompt. If you only need a short line on disk, that is put a short line into a leftover-box file. If you only need the names and sizes, that is see what's in a leftover-box folder. Skip this whole note if you only need a house share other computers browse. That is a folder the house can open.

What this is

chmod means change mode. It changes the leftover-box permission bits on a file you own. You run it on the leftover box, after SSH. It does not write the file's words. That is echo or nano. It does not change who owns the file. That owner job is a different tool, and you do not need it tonight. It does not open a permissions window. One short command, same leftover box, the run bit flipped on or off.

When ls -l prints a line, the first column looks like -rw-rw-r--. Those letters are read, write, and execute for you, for your group, and for everyone else. An x in that column means “may run.” A dash where the x would be means “may not.” That is the whole first-night story.

Make a practice script runnable

SSH in. Put one short practice script in home. A short name with no spaces is easier to type later:

echo '#!/bin/sh' > ~/hello.sh

echo 'echo hello from the leftover box' >> ~/hello.sh

The first line tells the leftover box this file is a shell script. The second line is the one short job. Peek:

cat ~/hello.sh

See the permission letters before you change them:

ls -l ~/hello.sh

You will usually see something like -rw-rw-r-- and no x. Trying to run it as a program fails until you flip that bit:

chmod +x ~/hello.sh

ls -l ~/hello.sh

You want an x in the first group of letters now, often -rwxrwxr-x or similar. Then run it by path:

~/hello.sh

You should see hello from the leftover box. That is the whole first-night trick.

Useful extras, still practicing only

Need the run bit off again after you practice?

chmod -x ~/hello.sh

ls -l ~/hello.sh

The x should be gone. The words inside the file are still there.

Need a private note that only you can read? Practice on a throwaway file, not on SSH settings:

echo 'practice secret' > ~/private.txt

chmod 600 ~/private.txt

ls -l ~/private.txt

You want something like -rw-------. The number 600 is a short form: you may read and write, nobody else may. Skip deeper number puzzles tonight. chmod +x and chmod 600 are enough for a first leftover box.

If the leftover box says command not found, install the usual tools, then try again:

sudo apt install coreutils

Debian and Ubuntu Server usually already have it. That install is not a reason to buy a permissions GUI.

When you are done practicing:

rm -i ~/hello.sh ~/private.txt

What this is not

This is not writing the words inside the file. That is put a short line into a leftover-box file or edit a leftover-box file from the couch. It is not listing names. That is see what's in a leftover-box folder. It is not changing who owns the file. Skip owner changes tonight. It is not turning off leftover-box password login. That is turn off leftover-box password login once the key works. It is not a house share other computers browse. That is a folder the house can open.

What next

Need a short line before the script exists? Put a short line into a leftover-box file. Need several lines in the editor? Edit a leftover-box file from the couch. Need the names and letters again? See what's in a leftover-box folder. Need a second name that still points at the same file? Make a leftover-box shortcut. Need a folder for scripts to land in? Make a leftover-box folder. Need a file from the laptop instead? Copy a file to the leftover box from your laptop. When a house job broke, look at the leftover box's own diary: when something broke, look at the leftover-box log. When key login is boring on every computer you use, turn off leftover-box password login once the key works. Keep SSH on the house network: keep the leftover box on the house network. Do not forward port 22.

Skip

• Skip if SSH still fails. Finish SSH from the couch first.
• Skip chmod -R, chmod on anything under /etc, SSH settings, or a file you care about. Practice only in home tonight.
• Skip changing file owners, setuid bits, and ACL tools on night one. The run bit and 600 are the job.
• Skip leftover-box SSH settings, /etc/shadow, and anything under /etc/ssh. Looking at trusted laptop keys is see which laptop keys the leftover box already trusts.
• Skip buying a permissions GUI, Midnight Commander, or a NAS to flip one leftover-box run bit.
• Skip opening SSH to the internet so you can change permissions from a coffee shop. That is keep the leftover box on the house network.