Hands-on Lab·Red Hat Certified System Administrator
Group Membership Management
One objective, and one mistake worth more marks than the rest of the domain combined: `usermod -G` without `-a` replaces every secondary group instead of adding one, reports nothing, and exits 0. It is captured happening. The guide also builds the shared directory that group tasks usually want.
Users and Groups Guide 19 of 67 Intermediate
- OSRHEL 10.0 (Coughlan)
- Kernel6.12.0-55.9.1.el10_0
- dnf4.20.0
- Flatpak1.16.0
- TimeAbout 15 min
- Reviewed23 August 2026
Written against the versions above. Red Hat uses the **user private group** scheme: `useradd bob` also creates a group `bob` and makes it his primary. That is why a home directory can be `bob:bob` and why `umask 002` is safe here - the group is a group of one.
| Server Name | IP Address | OS | Roles | CPU | RAM | HDD |
|---|---|---|---|---|---|---|
| RHCSA-A01 | 192.168.0.31 | RHEL 10.0 (Coughlan) | Practice node (graded) - spare /dev/sda | 2 Core | 4 GB | 50 GB + 15 GB |
Before you start
- A sudo-capable account.
- The session creates and removes a user, two groups and
/srv/shared.
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Primary and secondary
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Creating and renaming groups
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Adding a user to groups
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The missing letter
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The primary group decides file ownership
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A shared directory with SGID
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Removing membership and groups