User Management

What is a user?

• Nothing more than a number (user ID - UID)
• Everything else revolves around this number
• System maps UID to additional set of information based on an API.

/etc/passwd

• login names: ≤ 32 chars, case sensitive and (in some cases) even special chars (☹, …)
• encrypted password ( or *) - do NOT leave empty
  • DES, MD5($1$..), Blowfish($2y$), SHA-256 ($5$), SHA-512 ($6$),
  • check /etc/login.defs or (was) /etc/default/passwd plus PAM and on RHEL/CentoS authconfig.
• UID (32-bit integer)
  • 0 for root by default
  • do not recycle them (or as late as possible) - ? why
  • should be unique in the whole organization ( else NFS problems, ..)
• GID
• GECOS (finger’s interpretation)
• home dir
• login shell

/etc/group

• Contains the names of UNIX groups and list of each group’s members

System utility commands

• useradd
• userdel
• usermod
• pwconv
• pwunconv
• groupadd
• groupmod
• groupdel