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Today i just got a question on how actually a useradd command works and is it possible for us to create user without useradd command. And here is my answer after some googling around 😆

what is useradd ?

useradd COMMAND:
useradd – Adds new user to the linux system, with specified user-name. When a new user is added then a corresponding entry is made in files /etc/passwd, /etc/group and /etc/shadow

SYNTAX:
The Syntax is
useradd [options] [username]

OPTIONS:

# useradd –help

Usage: useradd [options] LOGIN

Options:

EXAMPLE:

1. To add new user:

   # useradd test

   This command will add a new user with name test.

2. To add user but not allow to login in the system:

   useradd -s /bin/nologin test

   This command will add user hiox but not allow to login. Or you can go to the /etc/passwd and set the test username  Shell access tobe /usr/sbin/nologin or /usr/sbinfalse

   Understanding fields in /etc/passwd

   The /etc/passwd contains one entry per line for each user (or user account) of the system. All fields are separated by a colon (:) symbol. Total seven fields as follows.

   Generally, passwd file entry looks as follows (click to enlarge image):

   

   1. Username: It is used when user logs in. It should be between 1 and 32 characters in length.
   2. Password: An x character indicates that encrypted password is stored in /etc/shadow file.
   3. User ID (UID): Each user must be assigned a user ID (UID). UID 0 (zero) is reserved for root and UIDs 1-99 are reserved for other predefined accounts. Further UID 100-999 are reserved by system for administrative and system accounts/groups.
   4. Group ID (GID): The primary group ID (stored in /etc/group file)
   5. User ID Info: The comment field. It allow you to add extra information about the users such as user’s full name, phone number etc. This field use by finger command.
   6. Home directory: The absolute path to the directory the user will be in when they log in. If this directory does not exists then users directory becomes /
   7. Command/shell: The absolute path of a command or shell (/bin/bash). Typically, this is a shell. Please note that it does not have to be a shell.

   In above command:
   test	-Is the user-name
   /bin/nologin	-Is Shell assigned to the user

3. To set expire date of the user:

   useradd -e 2008-06-30 test

   This command will add user test and set the expire date to 2009-06-30.

   In above command:
   test	-Is the user-name
   2009-06-30	-Is date on which the user-account will be expired

4. To create user without creating home directory:

   useradd -M test

   The above command will create user test but home directory will not be created.

How to add user without useradd command ?

as you probably know useradd command actualy create a user on /etc/passwd to determine the user id home directory comman shell etc, /etc/group to determine te group id and /etc/shadow for password. I will create a newtest username but since the password was encrpty MD5 i will use the previous username password on the newtest username that we will create withiut useradd command

# useradd testing
# passwd testing
New password: password
Re-enter new password: password
Password changed.
#
# cat /etc/shadow | grep testing
testing:$1$AdHBr9EJ$VwEqlF.GprlX28oWWYprZ0:14313:0:99999:7:::
#
# cat /etc/passwd | grep testing
testing:x:1001:1001::/home/tesing:/bin/sh
# cat /etc/group | grep testing
testing:x:1001:

Create newtest username without adduser command
# vi /etc/shadow
add newtest password and save
newtest:$1$AdHBr9EJ$VwEqlF.GprlX28oWWYprZ0:14313:0:99999:7:::
# vi /etc/group
add newtest username group and id (makesure u have use the new id number
newtest:x:1002:
# vi /etc/passwd
add newtest username,id,home directory ,shell command
newtest:x:1002:1002::/home:/bin/sh

Of course, this is my version of creating a user without useradd command. Please correct me if i am wrong

Enable mod_rewrite on Apache

Simply, mod_rewrite is used for rewriting a URL at the server level, giving the user output for that final page. So, for example, a user may ask for http://www.somesite.com/widgets/blue/, but will really be given http://www.somesite.com/widgets.php?colour=blue by the server. Of course, the user will be none the wiser to this little bit of chicanery.

an Apache web server module installed on all of our Linux servers by default; it does not have to be installed or enabled. In case you haven’t isntalled it you can try this

# sudo a2enmod rewrite

Enable mod_headers on Apache

For customization of HTTP request and response headers, you should enable mod_headers on Apache.

sudo a2enmod headers

Enable mod_expires on Apache
a module that allows you to set a given period of time to live for web pages and other objects served from web pages. The idea is to inform proxies like Squid and web browser how often they should reload objects from the server. This will have you bandwidth and server load, because clients who follow the header will reload objects less frequently.

# sudo a2enmod expires

Then reload your apache
# /etc/init.d/apache2 force-reload