How to a Add and Remove User Account on RHEL 6/7, CentOS 6/7, Oracle Linux 6/7

This article will explain and share how to add and remove user account with useradd(add) and userdel (remove) from the command-line on linux RHEL 6/7, CentOS 6/7, Oracle Linux 6/7 server.

1. Adding a New User to an Linux System.

a) Get the useradd manual :

# man useradd
useradd - create a new user or update default new user information

b) To creates the new account and the /home/john home directory :

# useradd --home /home/ehowstuff ehowstuff

c) useraddd command does not set any valid password by default, and user cannot log in until a password is set.To set the password user the following command :

# passwd ehowstuff
Changing password for user ehowstuff.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.

d) Verify the values in /etc/password :

# cat /etc/passwd | grep ehowstuff
ehowstuff:x:501:501::/home/ehowstuff:/bin/bash

e) Verify the values in /etc/group :

# cat /etc/group | grep ehowstuff
ehowstuff:x:501:

f) Verify email user created for id ehowstuff :

# ls /var/spool/mail | grep ehowstuff
ehowstuff

More useradd options :

-c, –comment COMMENT
Add a value, such as a full name, to the GECOS field.

-g, –gid GROUP
Specify the primary group for the user account.

-G, –groups GROUPS
Specify a list if supplementary groups for the user account.

-a, –append
Used with the -G option to append the user to the supplemental groups mentioned without removing the user from other groups.

-d, –home HOME_DIR
Specify a new home directory to a new location. Must be used with the -d option.

-m, –move-home
Move a user home directory to a new location. Must be used with the -d option.

-s, –shell SHELL
Specify a new login shell for the user account.

-L, –lock
Lock a user account.

-U, –unlock
Unlock a user account.

2. Deleting a User from an Linux System.

a) Get userdel manual :

# man userdel
userdel - delete a user account and related files

b) userdel username removes the user from /etc/passwd, but leaves the home directory intact by default. Proper command to remove the user’s account, user’s home directory and mail spool as part of the deletion process :

# userdel --remove ehowstuff

or

# userdel -r ehowstuff

Warning :
When a user is removed with userdel without the -r option specified, the system will have files that are owned by an unassigned user ID number. This can also happen when files created by a deleted user exist outside their home directory. This situation can lead to information leakage and other security issues.

 

How to Increase PHP File Upload Size Limit

Q. When you try to update the blog post in WordPress or any php application, you might notice that the application such as WordPress has a prohibitive maximum PHP file upload size. How to increase this limit in PHP ? In the below screenshot, i configured my PHP upload size to 50MB.

PHP file upload

A. If you own the virtual private server of dedicated web server, it is very easy to increase this parameter or option. The options can be set in php.ini configuration file, this configuration apply to all your applications. Many shared hosting server allows a maximum PHP file upload size is very low. This method may not work for most shared hosting because you do not give root access. If you plan to receive larger files, you should consider to purchase virtual private server (VPS) or dedicated server hardware.

What is default PHP File Upload Size (upload_max_filesize)?

The default values for PHP will restrict you to a maximum 2 MB upload file size.

Note : Below require you to access the server using root access from the linux server console. The steps has been tested on PHP 5.3 and PHP 5.4.

a) Login to your server via ssh connection.

b) Open php.ini file using vi editor :

# vi /etc/php.ini

There are two PHP configuration options that control the maximum PHP file upload size which are “upload_max_filesize” and “post_max_size”.

By default post_max_size = 8M and upload_max_filesize = 2M. You can update this value to the following :

c) Update this value from 8M to 60M :

post_max_size = 60M

d) Update this value from 2M to 50M :

upload_max_filesize = 50M

Note : Technically, post_max_size should always be greater than upload_max_file size . But for such a large number 150M you can safely make them the same size.

e) After you have made a changes, Then restart your web server to take effect of new PHP file upload size (e.g Apache or Nginx).

You can read more on these posts which explains PHP file upload article.

How to Install and Configure TigerVNC Server on CentOS 7.1 / RHEL 7.1 / Oracle Linux 7

The following article explain how to Install and configure TigerVNC Server on CentOS 7.1 or Red Hat Enterprise Linux (RHEL 7.1) or Oracle Linux 7. TigerVNC (Tiger Virtual Network Computing) is a remote access utility that allows you to control other computers that running graphical desktop sharing in separate sessions in parallel. It is works on the client-server principle: a server shares its output (vncserver) and a client (vncviewer) connects to the server. TigerVNC in RHEL 7 or CentOS 7 or Oracle Linux 7 uses the systemd system management daemon for its configuration. The /etc/sysconfig/vncserver configuration file has been replaced by /etc/systemd/system/vncserver@.service.

Install and Configure TigerVNC Server on Linux

1. Install tigervnc-server

# yum install tigervnc-server -y

2. Copy this file to /etc/systemd/system/vncserver@:.service :

# cp /lib/systemd/system/vncserver@.service /etc/systemd/system/vncserver@:1.service

3. Edit and vncserver parameters appropriately

# vi /etc/systemd/system/vncserver@:1.service

Replace with actual user hat exist on the linux (e.g ehowstuff)

[Unit]
Description=Remote desktop service (VNC)
After=syslog.target network.target

[Service]
Type=forking
# Clean any existing files in /tmp/.X11-unix environment
ExecStartPre=/bin/sh -c '/usr/bin/vncserver -kill %i > /dev/null 2>&1 || :'
ExecStart=/sbin/runuser -l ehowstuff -c "/usr/bin/vncserver %i"
PIDFile=/home/ehowstuff/.vnc/%H%i.pid
ExecStop=/bin/sh -c '/usr/bin/vncserver -kill %i > /dev/null 2>&1 || :'

[Install]
WantedBy=multi-user.target

4. Run `systemctl daemon-reload` to make the changes take effect immediately :

# systemctl daemon-reload

5. Set the password for the user or users defined in the configuration file. Note that you need to switch from root to USER first.

# su - ehowstuff
$ vncpasswd
Password:
Verify:

6. To start the service, specify the display number directly in the command :

# systemctl start vncserver@:1.service

7. Enable the service to start automatically at system start

# systemctl enable vncserver@:1.service

8. Add firewall rules to allow the VNC connection :

# firewall-cmd --permanent --zone=public --add-port 5901/tcp
# systemctl restart firewalld.service

9. Run VNC viewer :
Configure TigerVNC Server