Finger displays:

Login – This is the username that is used to authenticate to
the system.

Name – This is the user’s full name.

Directory – This is the user’s home directory.

Shell – This is the default shell that will be provided to
that user.

Last Login – This displays the last time the user logged in
and where from.

 

id Username - Displays user information (
uid, gid, groups, etc)

 

/etc/passwd – This file contains the user account
information for your system.

/etc/shadow – This file contains passwords for your user
accounts.

/etc/group – This file contains your system’s groups.

 

/etc/passwd

username:password:UID:GID:Full_Name:Home_Directory:Default_Shell

 

• Username:
  The username field simply identifies the username the user will supply
  when logging in to the system.
• Password:
  This is a legacy field. At one time, the user’s password was stored in
  encrypted form in this field in the passwd file. However, for security
  reasons, the password has been moved from /etc/passwd to /etc/shadow.
• UID:
  This is the user ID for the user account. We discussed the UID earlier in
  this chapter.
• GID:
  This field references the group ID number of the user’s default group.
• Full_Name:
  This field contains the user’s full name.
• Home_Directory:
  This field contains the path to the user’s home directory.
• Default_Shell:
  This field specifies the shell that will be used by default.

 

/etc/shadow

Username:Password:Last_Modified:Min_Days:Max_Days:Days_Warn:Disabled_Days:Expire

 

• Username:
  This is the user’s login name from /etc/passwd.
• Password:
  This is the user’s password in encrypted format.( Accounts that have a *
  means they can’t log into the system )
• Last_Modified:
  This field displays the number of days since January 1, 1970 that the
  password was last changed.
• Min_Days:
  This field displays the minimum number of days required before a password
  can be changed.
• Max_Days:
  This field displays the maximum number of days before a password must be
  changed.
• Days_Warn:
  This field displays the number of days prior to password expiration that
  the user will be warned of the pending expiration.
• Disabled_Days:
  This field displays the number of days to wait after a password has
  expired to disable the account.
• Expire:
  This field displays the number of days since January 1, 1970 after which
  the account will be disabled.

 

 

Pwck – This
command is used to check if both the /etc/passwd and /etc/shadow files are
correct and working fine.

 

Pwconv - This
command will add any missing user account from /etc/passwd to /etc/shadow.

 

useradd – create
a new user or update default new user information.

 

Default Configuration files for useradd:

• /etc/default/useradd – This file
  contains defaults used by the useradd utility.
• /etc/login.defs – This file
  contains values that can be used for the GID and UID parameters when
  creating an account with useradd. It also contains defaults for creating
  passwords in /etc/shadow.

useradd Options:

-c Includes the users full name

-e Specifies the date when the user account will be disabled.
Format the date as yyyy-mm-dd.

-f Specified the number of days after password expiration before
the account is disabled. Use a value of 01 to disable this functionality.

-g Specifies the user’s default group.

-G Specifies additional groups that the user is to be made a member
of.

-M Specifies that the user account be created without a home
directory.

-m Specifies the user’s home directory.

-n Used only on Red Hat or Fedora system. By default, these systems
create a new group with the same name as the user every time an account is
created. Using this option will turn off this functionality.

-p Specifies the user’s password

-r Specifies that the user being created is a system user.

-s Specifies the default shell for the user.

-u Manually specifies a UID for the user.

 

Passwd - used to add and change passwords. Also can check status of
account.

To check password status of a
account type passwd -S username.

 

Passwd options:

-l Locks the user’s account. This option invalidates the user’s
password.

-u Unlocks a user’s account

-d Removes a user’s password.

-n Sets the minimum number of days required before a password can
be changed.

-x Sets the maximum number of days before a password must be
changed.

-w Sets the number of days prior to password expiration when the
user will be warned of the pending expiration.

-i Sets the number of days to wait after a password has expired to
disable the account.

 

Usermod - Utility to modify user accounts.

 

Usermod options:

-c Edits the user’s full name.

-e Sets the date when the user account will be disabled. Format the
date as yyyy-mm-dd.

-f Sets the number of days after password expiration before the
account is disabled. Use a value of -1 to disable this functionality.

-g Sets the users’s default group.

-G Specifies additional groups that the user is to be made a member
of.

-l Changes the username.

-L Locks the user’s account. This option invalidates the user’s
password.

-m Sets the user’s home directory.

-p Sets the user’s password.

-s Specifies the default shell for the user.

-u Sets the UID for the user.

-U Unlocks a user’s account that has been locked.

 

/etc/group – File where groups are set.

Group:Password:GID:Users

 

Group: Specifies the name of the group.

Password: Specifies the group password.

GID: Specifies the group ID (GID) number of the group.

Users: Lists the members of the group.

 

/etc/gshadow – File to define group password encrypted.

Group_Name:Password:Group_Admins:Group_Members

 

Groupadd - used to create a group.

 

Groupadd options:

-g Specifies a GID for the new group.

-p Specifies a password for the group.

-r Specifies that the group being created is a system group.

 

Groupmod - Modify the group settings, add users, and remove users.

 

Groupmod options:

-g Changes the group’s GID number.

-p Changes the group’s password.

-A Adds a user account to the group.

-R Removes a user account from the group.

 

Groupdel - Used to remove a group from the system.

 

Permissions:

Read – 4

Write – 2

Execute – 1

 

Chmod entity=permissions filename

U = Owner

G = Group

O = Other

Example: chmod u=rw,g=rw,o=r file.txt

 

You can use the minus and plug
sign to remove and add a permission.

Exmaple: chmod u-w file.txt This would remove the write permission for
owner.

 

Special Permissions:

SUID – 4

SGID – 2

Sticky Bit – 1

 

Permission	Description	Effect on Files	Effect on Directories
SUID	Set User ID Can only be applied to binary executable files (not shell scripts).	When an executable file with the SUID set is run, the user who ran the file temporarily becomes the file’s owner.	None.
SGID	Set Group ID Can be applied to binary executable files (not shell scripts).	When a user runs an executable file with the SGID set, the user temporarily becomes a member of the file’s owning group.	When a user creates a file in a directory that has SGID set, the file’s owner is set to the user’s account (as per normal). However, the owning group assigned to the new file is set to the owning group of the parent directory.
Sticky Bit		None.	When the Sticky Bit is assigned to a directory, users can only delete files within the directory for which they are the owner of the file or the directory itself. The negates the effect of having the write permission to a directory which could allow a user to delete files in a directory that he or she doesn’t own.

 

 

Managing Disk Quotas!

To check if you have the quota package installed on a
redhat/fedora system type rpm -qi quota
at the command prompt.

 

You MUST mount the filesystem with the quota options. The
quota options you must add in your /etc/fstab file are usrquota and grpquota.
After you edit your fstab file with these options restart your system.

 

Quotacheck - scan
a filesystem for disk usage, create, check and repair quota files.

Options:

            -a Checks all mounted file systems

            -m Forces check on mounted file
systems.

            -u Checks users.

            -g Checks groups.

            -v Operates in verbose mode.

 

To enable quota type quotaon
-av.

 

To view current disk space used by your users type repquota -av.

 

To create a disk quotq type edquota -u username.

 

You can enter edquota
-p source_user destination_user to copy quotas from one user to another.