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SYS-C0003 · Linux Users & Permissions

Special Permissions: SUID, SGID, Sticky Bit

Read one special mode. SUID is 4, SGID is 2, and sticky is 1. Do not set SUID on a shell.

Updated 25 October 2026 · Explainer

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

The calculator puts 4, 2, or 1 in front of the usual three digits. SUID runs a file as its owner. SGID does that for the group, and on a directory it keeps the group of new files. Sticky on a directory lets a user delete only their own files.

Do not set SUID on a shell or on a copy of a shell. Do not hunt the host for SUID files in order to misuse one. One file you administer, and a reason you can say. The tool drafts chmod. It does not change the file.

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.

  1. Name the file.
  2. Pick suid, sgid, or sticky.
  3. Read the four-digit mode.
  4. Reject a shell.
  5. Do not chmod during the reading.
  6. Stop.

Mistakes that outlive the command

Special Permissions: SUID, SGID, Sticky Bit goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.

Decisions to write down

One decision for Special Permissions: SUID, SGID, Sticky Bit: One file. The leading digit is 4, 2, or 1 on purpose. It is not a shell. Nothing was changed. And the host is yours.

Checks before you call it done

Confirm this before you call the change done: The file is written. The leading digit is written. A shell was refused. Nothing was changed. And the host is yours. If one of those fails, stop.

# SUID 4, SGID 2, sticky 1.
# Do not set SUID on a shell.
# Do not chmod during the reading.

Before you leave the host

Special Permissions: SUID, SGID, Sticky Bit 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.

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