Page 163 - DCAP602_NETWORK_OPERATING_SYSTEMS_I

Unit 9: File System Commands

3. The number of days (since January 1, 1970) since the password was last changed. notes
4. The number of days before password may be changed (0 indicates it may be changed at
any time).
5. The number of days after which password must be changed (99999 indicates user can keep
his or her password unchanged for many, many years).

6. The number of days to warn user of an expiring password (7 for a full week).
7. The number of days after password expires that account is disabled.
8. The number of days since January 1, 1970 that an account has been disabled.
9. A reserved field for possible future use.

Note All fields are separated by a colon (:) symbol. It contains one entry per line for
each user listed in /etc/passwd file.

9.1.3 the /etc/group file

In Linux systems, multiple users can be categorized into groups. Users on Linux systems are
assigned to one or more groups for following reasons:
To share files or other resource with a small number of users:
1. Ease of user management
2. Ease of user monitoring

3. Group membership is perfect solution for large Linux installation.
4. Group membership gives you or your user special access to files and directories or devices
which are permitted to that group

In Linux systems, every user must be a member of at least one group, which is identified by the
numeric GID of the user’s entry in /etc/passwd. This group is referred to as the primary group
ID. A user may be listed as members of additional groups in the relevant groups entry in the /
etc/group; the IDs of these groups are referred to as supplementary group IDs.
etc/group is a text file which defines the groups to which users belong under Linux and UNIX
operating system. Under Unix / Linux multiple users can be categorized into groups. Unix file
system permissions are organized into three classes, user, group, and others. The use of groups
allows additional abilities to be delegated in an organized fashion, such as access to disks, printers,
and other peripherals. This method, amongst others, also enables the Superuser to delegate some
administrative tasks to normal users.

The /etc/group file contains the database that lists every group on your computer and its
corresponding GID. Its format is similar to the format used by the /etc/passwd file.
It stores group information or defines the user groups i.e. it defines the groups to which users
belong. There is one entry per line, and each line has the format (all fields are separated by a
colon (:)
Consider following /etc/group line:

cdrom:x: 24:vivek,student13,raj
group_name: It is the name of group. If you run ls -l command, you will see this name printed in
the group field.

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