07-Accounts

07-Accounts - CSE 265: System and Network Administration...

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Spring 2006 CSE 265: System and Network Administration ©2006 Brian D. Davison CSE 265: CSE 265: System and Network Administration System and Network Administration User accounts The /etc/passwd file The /etc/shadow file The /etc/group file Adding users Removing users Disabling logins Account management utilities Root powers Ownership of files and processes The superuser Choosing a root password Becoming root Other pseudo-users
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Spring 2006 CSE 265: System and Network Administration ©2006 Brian D. Davison The /etc/passwd file The /etc/passwd file /etc/passwd lists all recognized users, and contains: login name encrypted password (unless /etc/shadow used) UID number default GID number full name, office, extension, home phone (optional) home directory login shell Examples root:lga4FjuGpZ2so:0:0:The System,,x6096,:/:/bin/csh jl:x:100:0:Jim Lane,ECT8-3,,:/staff/fl:/bin/sh
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Spring 2006 CSE 265: System and Network Administration ©2006 Brian D. Davison Login name Login name Syntax usernames must be unique <= 32 chars (old system limit 8 chars) any characters except newlines and colons Recommendations use lower case (even though case sensitive) choose easy to remember avoid “ handles” and cutesy nicknames
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Spring 2006 CSE 265: System and Network Administration ©2006 Brian D. Davison Encrypted passwords Encrypted passwords Most passwords are in /etc/shadow, not /etc/passwd Passwords are stored encrypted Cannot be changed by hand Can be copied from another account Are set using passwd (or yppasswd for NIS) Passwords should never be left blank Put a star (*) in place (x for shadow usage) Otherwise no pw needed! MD5 passwords (standard on RH) can be any length Other systems only use the first eight characters
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Spring 2006 CSE 265: System and Network Administration ©2006 Brian D. Davison UID number UID number In Linux, UIDs are unsigned 32-bit integers (4B!) Older systems only allowed up to 32,767 Root is UID 0 Fake/system logins typically have low UIDs Place real users >= 100 Avoid recycling UIDs Old files, backups are identified by UID Preserve unique UIDs across org helpful for NFS
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Spring 2006 CSE 265: System and Network Administration ©2006 Brian D. Davison Other fields Other fields default GID number like UIDs, 32-bit unsigned integers GID – is for the group “ root” GECOS fields (optional) [chfn] General Electric Comprehensive OS full name, office, extension, home phone home directory Where the user starts when the log in login shell [chsh] such as sh/bash, csh/tcsh, ksh, etc.
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Spring 2006 CSE 265: System and Network Administration ©2006 Brian D. Davison The /etc/shadow file The /etc/shadow file Readable only by superuser Enhanced account information Use is highly recommended Use usermod to
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07-Accounts - CSE 265: System and Network Administration...

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