This document discusses how to add new users and storage on a Linux system. It covers editing the /etc/passwd and /etc/shadow files to define a new user account, setting an initial password, creating the user's home directory, installing startup files, and setting permissions. The key steps are using a command like useradd to edit the password and shadow files, setting the password with passwd, creating the home directory, copying default startup files, and setting ownership of the home directory to the new user.

1. Adding New Users
and
Storage
Prepared By
Prof. Bhushan Pawar
www.bhushanpawar.com
Prof.Bhushan Pawar
www.bhushanpawar.com
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2. The /etc/passwd file
• /etc/passwd file is a list of users recognized by
the system.
• The system consults /etc/passwd at login time
to determine a user’s UID and home directory,
among other things.
Prof.Bhushan Pawar
www.bhushanpawar.com
2

3. Continue…
• It contains seven fields separated by colons:
• Login name
• Encrypted password
• UID (user ID) number
• Default GID (group ID) number
• “GECOS” information: full name, office,
extension, home phone
• Home directory
• Login shell
Prof.Bhushan Pawar
www.bhushanpawar.com
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4. Continue…
• E.g
root:x:0:0:The System,,x6096,:/:/bin/sh
- The passwd file contains an x in the encrypted
password field on Linux, Solaris.
• The actual encrypted passwords are stored in
/etc/shadow on Linux, Solaris.
Prof.Bhushan Pawar
www.bhushanpawar.com
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5. Login name
• Must be unique and, depending on the
operating system, may have length and
character set restrictions.
• Login names can never contain colons or
newlines because these characters are used as
field separators and entry separators.
Prof.Bhushan Pawar
www.bhushanpawar.com
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6. Continue…
Prof.Bhushan Pawar
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7. Encrypted password
• The encrypted password in the /etc/passwd
file
Prof.Bhushan Pawar
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8. UID (user ID) number
• UIDs are usually unsigned 32-bit integers.
• Root has UID 0.
Prof.Bhushan Pawar
www.bhushanpawar.com
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9. Default GID number
• A group ID number is a 32-bit integer.
• GID 0 is reserved for the group called root or
system.
• The /etc/group file defines the groups, with
the GID field in /etc/passwd providing a
default (or “effective”) GID at login time
Prof.Bhushan Pawar
www.bhushanpawar.com
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10. GECOS field
• The GECOS field is sometimes used to record
personal information about each user.
• The chfn command lets users change their
own GECOS information.
• On most systems chfn understands only the
/etc/passwd file
Prof.Bhushan Pawar
www.bhushanpawar.com
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11. Home directory
• If the home directory is missing at login time,
the system prints a message such as “no
home directory” and puts the user in /.
• On Linux, if /etc/login.defs sets
DEFAULT_HOME to no, the login is not
allowed to continue.
Prof.Bhushan Pawar
www.bhushanpawar.com
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12. Login shell
• The login shell is normally a command
interpreter such as the Bourne shell or the C
shell (/bin/sh or /bin/csh), but it can be any
program.
• sh is the traditional default for UNIX, and bash
(the GNU “Bourne again” shell) is the default
for Linux and Solaris.
• tcsh is an enhanced C shell with command
editing.
Prof.Bhushan Pawar
www.bhushanpawar.com
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13. THE /ETC/SHADOW AND
/ETC/SECURITY/PASSWD FILES
• A shadow password file is readable only by
the superuser and serves to keep encrypted
passwords.
• IBM calls the file that stores the encrypted
passwords /etc/security/passwd, while the
rest of the world calls it /etc/shadow.
Prof.Bhushan Pawar
www.bhushanpawar.com
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14. /etc/shadow
• The shadow file is not a superset of the
passwd file, and the passwd file is not
generated from it. We must maintain both
files or use tools such as useradd that
maintain both files on your behalf. Like
/etc/passwd, /etc/shadow contains one line
for each user. Each line contains nine fields,
separated by colons
Prof.Bhushan Pawar
www.bhushanpawar.com
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15. Continue…
• Login name
• Encrypted password
• Date of last password change
• Minimum number of days between password changes
• Maximum number of days between password changes
• Number of days in advance to warn users about password
expiration
• Linux: Days after password expiration that account is disabled
Solaris/HP-UX: Days before account automatically expires
• Account expiration date
• A reserved field that is currently always empty, except on
Solaris Prof.Bhushan Pawar
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16. THE /ETC/GROUP FILE
• The /etc/group file contains the names of UNIX
groups and a list of each group’s members.
• Each line represents one group and contains four
fields:
• Group name
• Encrypted password or a placeholder
• GID number
• List of members, separated by commas (be
careful not to add spaces)
Prof.Bhushan Pawar
www.bhushanpawar.com
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17. example
1. system:!:0:root,pconsole,esaadmin
2. staff:!:1:ipsec,esaadmin,trent,ben,garth,evi
3. bin:!:2:root,bin
4. sys:!:3:root,bin,sys
5. adm:!:4:bin,adm
6. nobody:!:4294967294:nobody,lpd
Prof.Bhushan Pawar
www.bhushanpawar.com
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18. ADDING USERS: THE BASIC STEPS
• The process of adding a new user consists of
several steps required by the system:
– Have the new user sign your policy agreement.
– Edit the passwd and shadow files to define the
user’s account.
– Add the user to the /etc/group file (not really
necessary, but nice).
– Set an initial password.
– Create, chown, and chmod the user’s home
directory.
– Configure roles and permissions
Prof.Bhushan Pawar
www.bhushanpawar.com
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19. Continue…
• For the user:
– Copy default startup files to the user’s home
directory.
– Set the user’s mail home and establish mail
aliases.
• For you:
– Verify that the account is set up correctly.
– Add the user’s contact information and account
status to your database
Prof.Bhushan Pawar
www.bhushanpawar.com
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20. Continue…
• You must be root to add a user, you must have
Admin privileges.
• This is a perfect place to use sudo.
• For this we can use “useradd” or “adduser”
command.
Prof.Bhushan Pawar
www.bhushanpawar.com
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21. Editing the passwd and group files
• If you have to add a user by hand, use vipw to
edit the passwd and shadow files.
• NOTE:-
– On Solaris, and Red Hat systems, vipw
automatically asks if you would like to edit the
shadow file after you have edited the passwd file.
SUSE and Ubuntu systems use vipw -s for this
function.
Prof.Bhushan Pawar
www.bhushanpawar.com
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22. Setting a password
• Set a password for the new user with
$ sudo passwd newusername
Prof.Bhushan Pawar
www.bhushanpawar.com
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23. Creating the home directory and
installing startup files
• You can create the new user’s home directory
with a simple mkdir.
• Startup files traditionally begin with a dot and
end with the letters rc, short for “run command,”
• The initial dot causes ls to hide these
“uninteresting” files from directory listings unless
the -a option is used.
• Sample startup files are traditionally kept in
/etc/skel (Linux, Solaris, HP-UX) or /etc
Prof.Bhushan Pawar
www.bhushanpawar.com
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24. Prof.Bhushan Pawar
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25. Setting permissions and ownerships
• The command
– $ sudo chown -R newuser:newgroup ~newuser
Prof.Bhushan Pawar
www.bhushanpawar.com
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26. Any Question???
• If you having any doubt then you can ask me
question on
bhushan.pawar@mescoepune.org
Or
contact me on (+91)-7588318728
Prof.Bhushan Pawar
www.bhushanpawar.com
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