Permissions and users · Lesson 31 of 33 · 8 minutes

SSH mode matrix

Compare directory and key-file modes used by an SSH account.

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learner@clairos:~ $

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Your objectives

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1
Inspect the SSH directory
Run stat ~/.ssh.
Hint & worked example
Inspect a file or directory metadata record, including ownership, permissions, and size.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
stat ~/.ssh
```
Remember: Metadata and file contents answer different questions.
2
Set the SSH directory mode
Run chmod 700 ~/.ssh.
Hint & worked example
Change permissions using an octal mode or a symbolic adjustment. Each rwx bit belongs to owner, group, or other.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
chmod 700 ~/.ssh
```
Remember: Do not use 777 as a blanket fix. Grant the smallest access needed.
3
Set the key-file mode
Run chmod 600 ~/.ssh/authorized_keys.
Hint & worked example
Change permissions using an octal mode or a symbolic adjustment. Each rwx bit belongs to owner, group, or other.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
chmod 600 ~/.ssh/authorized_keys
```
Remember: Do not use 777 as a blanket fix. Grant the smallest access needed.
4
Verify the key-file mode
Run stat ~/.ssh/authorized_keys.
Hint & worked example
Inspect a file or directory metadata record, including ownership, permissions, and size.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
stat ~/.ssh/authorized_keys
```
Remember: Metadata and file contents answer different questions.

Understand the pattern

Keeping SSH directories and key files appropriately restricted helps operators explain what they know before they change anything.

stat: Inspect a file or directory metadata record, including ownership, permissions, and size.
Metadata and file contents answer different questions.
chmod: Change permissions using an octal mode or a symbolic adjustment. Each rwx bit belongs to owner, group, or other.
Do not use 777 as a blanket fix. Grant the smallest access needed.

Worked example and expected result

$ stat ~/.ssh

Path: /home/learner/.ssh
Type: dir
Mode: drwx------
Owner: learner
Group: learners
Size: 3 items

Exit status: 0. The command completed successfully in the training fixture.

$ chmod 700 ~/.ssh

(no output; exit 0)

Exit status: 0. The command completed successfully in the training fixture.

$ chmod 600 ~/.ssh/authorized_keys

(no output; exit 0)

Exit status: 0. The command completed successfully in the training fixture.

$ stat ~/.ssh/authorized_keys

Path: /home/learner/.ssh/authorized_keys
Type: file
Mode: -rw-------
Owner: learner
Group: learners
Size: 40 bytes

Exit status: 0. The command completed successfully in the training fixture.

Try a variation

Repeat this workflow in the sandbox with a different scratch filename. Keep the system fixtures unchanged and compare the observed output with your expectation before moving on.

Explain it

In “SSH mode matrix”, which interpretation is safe?Do not use 777 as a blanket fix. Grant the smallest access needed.A command appearing in history proves it completed successfully.A successful first check guarantees that every dependent service is healthy.

Apply it elsewhere

Before adapting the chmod workflow from “SSH mode matrix” to another server, what should you do?Paste the training paths unchanged into production.Skip output inspection whenever the command is familiar.Confirm the current directory, target identity, permissions, and the installed command behavior first.

Keep the momentum.

Complete the lab, then explain and apply the pattern.

Next: Service account ownership Try an incident drill

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