Linux › Section G · System configuration › Topic G.7
User IDs and user access
The kernel does not know names, only numbers. Understanding how a login becomes a set of numeric IDs, how a process can hold more than one of them, and how to see who is on the machine is the key to explaining both everyday permissions and privilege escalation.
In this topic
- Numbers underneath the names
- Looking at identities: id, whoami, groups
- Where lookups come from: nsswitch
- Worked example: reading id to predict access
- Real, effective and saved UIDs
- Switching users: su and sudo
- Who is on the system: who, w, last
- Worked example: reading login records
- Identify, authenticate, authorise
- Common mistakes to avoid
- Key takeaways
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