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Security in depth · Unit 22 · Lesson 2 of 44
Linux process identity
Use a process credential snapshot to explain a file-access decision.
Helpful before thisLinux privilege escalation
After this lesson you can
- Identify the credentials relevant to an ordinary Linux file-read check.
One idea. One situation. One reasoned decision.
How it works
Linux checks credentials attached to the process performing an operation. A real user ID identifies the process owner; effective IDs influence many permission decisions. For file access, Linux uses filesystem IDs plus supplementary groups. Filesystem IDs normally match effective IDs, but they can differ. A process ID identifies an instance, not its permission level.
Read the supplied record
R1 describes a fictional summary worker at the moment it requests a file read.
| Field | Supplied value |
|---|---|
| Dashboard label | Summary helper |
| Real, effective, filesystem user | report-worker |
| Filesystem group | reports |
| Supplementary groups | reviewers |
| File owner / group | archivist / reviewers |
| File permissions | Owner read/write; group read; other none |
Assume ordinary file permissions, no extended ACL or overriding capability, searchable parent directories, no additional blocking policy, and a newly requested read. The worker is not the file owner. Its supplementary reviewers membership selects a matching group class that permits read. The friendly dashboard label contributes no permission.
Changing the account’s group list in a directory does not, by itself, prove that an already-running worker’s credential snapshot changed. A reviewed restart or other supported transition needs its own resulting evidence.
The snapshot establishes this read decision under these assumptions. It does not prove permission to write, access another resource, or perform every operation as the human who launched the job. Record the process instance and observation time so a later service replacement is not confused with this one.
The key distinction: Review the acting process's credentials, not just its account label.
Check yourself
No timer. No penalties. Read the explanation and try again whenever you like.
This lesson’s questions have changed. Your reading progress is saved; review the updated questions.
-
Under R1, why can the worker read the reviewers file?
Show the answer
Correct answer: Its supplementary reviewers group matches the file group and grants read. The filesystem identity is not the owner, so the matching group class applies under the stated ordinary permission assumptions.
Try it
- WriteWrite a three-line review of R1: which identity fields matter for the read, why the group grant applies, and what evidence would be needed after a service identity change.