Account Considerations

Information to Plan Before Creating a User : Username, UID, Primary group, Supplementary groups, Home directory, Skeleton directory, Shell, Comment (GECOS)

Category Key Points Example Command
Username Required for useradd
First char: _ or a–z
Max: 32 (≤16 recommended)
Allowed: letters, numbers, -, _
Last char: not -
Must be unique		 useradd jane
User Identifier (UID) Auto-increment by default
Set manually with -u
Recommended max: 60000
root UID = 0
System: 1–999
Regular users: ≥1000		 useradd -u 1000 jane

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Group Type Description Command
Primary Group Default group if not specified
UPG: group auto-created
Non-UPG: usually users (GID 100)
Set with -g		 useradd -g users jane
Supplementary Groups Extra group memberships
Comma-separated list
Set with -G		 useradd -G sales,research jane

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Item Description Command
Home Directory Default: /home/username
Created automatically if enabled

Controlled by /etc/default/useradd and /etc/login.defs

Options :
-m create home
-M do not create home
-b set base directory
-d set full path		 useradd -m jane
useradd -mb /test jane
useradd -md /test/jane jane
Skeleton Directory Default: /etc/skel
Files copied to home
-k set custom skeleton
Requires -m		 useradd -mk /home/sysadmin jane

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Item Description Command
Shell Default from /etc/default/useradd
Override with -s
System accounts often use /sbin/nologin		 useradd -s /bin/bash jane
Comment (GECOS) Usually full name
Shown by login managers
Set with -c		 useradd -c "Jane Doe" jane