This is an original planning guide. It is not a vendor manual, an official standard, or legal advice. Example addresses use documentation ranges. Review every command before you paste it.
What this hour is for
This sheet is a lookup. 644, 755, 640, and 600 cover the files an admin actually sets. The chmod calculator shows the same bits. It does not change a file.
A directory needs the execute bit to be entered. A file needs execute only if it is a program. Those are different rows. Do not copy a directory mode onto a private key.
The owner, the group, and everyone else are three numbers. If you cannot say who everyone else is, the mode is too open. 192.0.2.10/24 and example.com are documentation. They stay in the note.
The change you can finish
Apply nothing while you are writing the note. When the lab window opens, it is one change on the host named in the ticket. Read the draft, then the host, then decide.
Rollback is the file, the package version, or the snapshot you saved first. You do not invent a rollback after the only copy is gone.
- Name the file and who must read it.
- Look up one mode.
- Read the symbolic form beside the number.
- Reject 777.
- Do not apply it during the reading.
- Stop.
Mistakes that outlive the command
Linux Permissions Cheat Sheet goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.
- 777 used as a test.
- A directory mode copied onto a key.
- The sheet used as a permission design for a whole tree.
- A special bit set from memory.
Decisions to write down
One decision for Linux Permissions Cheat Sheet: One file is this lookup. The number and the symbolic form match. 777 is rejected. And the calculator did not change a host.
Checks before you call it done
Confirm this before you call the change done: The mode is written. The symbolic form matches. 777 was not chosen. No host was changed. And the path is named. If one of those fails, stop.
| Mode | Usual file | Not for |
|---|---|---|
| 644 | A file others may read | A private key |
| 755 | A directory or a program | A secret |
| 600 | A key or a credential file | A shared document |
| 640 | A file the group may read | The whole disk |
644 file. 755 directory. 600 private.
777 is not on this sheet.Before you leave the host
Linux Permissions Cheat Sheet ends when the hostname in the prompt matches the hostname in the ticket. If it does not, you are on the wrong host. Stop. A command that succeeded on the wrong host is not progress.
The draft stays a draft until a person has read the names in it. A generator does not log into the host and does not know which disk is empty. You delete a line that names a host, a path, or an account you did not write down.
192.0.2.10/24, gateway 192.0.2.1, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. example.com is a documentation name. They belong in the note. They are not values you leave on a host because a draft included them.
prompt-for-this is a reminder that a secret is missing. It is not a password, a key, or a token you save in the ticket or in git. The real secret stays in the password store.
One change is the window. If two things move and the result is wrong, you will not know which one did it. The next change waits for its own page.
If the same step fails twice, stop for the day. The failure is the result. Adding a forum command beside a half-applied change produces a host nobody can rebuild. Restore the copy you took first.
A second person reads the hostname and the change aloud. If they cannot find them in the ticket, the note is not done. Silence is not agreement. Then leave the host alone.
This page is a planning guide. It is not a vendor manual, not an official standard, and not permission to touch a host you do not administer. You do not disable a firewall, AppArmor, or SELinux to make a check pass.
Tools for this guide
These tools run in the browser on this site. They do not log into your machines.
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