Posted in Linux, Security

Access Control List (ACL) Permissions in RHEL 7/Centos 7

Today I am going to show you how to use access control list (ACL) permissions in rhel7. Traditionally we have assigned permission to one user/owner and one group for file or directory but in some cases we need other user or other group apart from owner need to have readonly access or write access on same directory. To achieve this we have access control list permission concept in Linux.

Other users and and groups can also access file or directory even when they are not owners and member of group who is having ownership on that file or directory.

we use only two commands getfacl to see ACL permissions on directory/file and setfacl to set ACL permissions. We can even set default ACL so that new files and sub-directories created in directory will inherit ACL permissions of parent directory.

The filesystem needs to be mounted with ACL support enabled. XFS filesystems have built-in ACL support and Ext4 filesystem in RHEL7 have ACL option enabled by default. In earlier versions of RHEL you may need the ACL option included with mount request.

First we see ACL permission on file named prod.conf.

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Posted in Linux

Manage local Users and Groups in Centos 7/RHEL 7

1.  To create user use command useradd.

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2. Whenever new user is created without specifying any other values then default values will be taken after creating user. You can check default values for any user creation using following commands.

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user chris is created with id 1001 and user private group created named chris with 1001 group id (the group created with same name as user is called user private group).

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Posted in Linux

How to turn off GUI screen lock on rhel 7/centos 7

It was very annoying when I work on rhel 7 and screen gets locked when it was idle for some period and again I have to logged in from virtual box and then on server. I search on web to turn off screen lock on rhel 7 and it was hard to find out.
rhel 7 have different options to turn off screen than in previous versions.
So I thought to create this post so that people can easily turn off their screen lock without wasting their time searching for it.

1. Open the rhel 7 GUI. In Applications go to System Tools.5

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Posted in Linux

How to change the grub timeout in rhel 7

Modification of boot time (grub timeout) is little different in rhel 7. Grub timeout is time to wait for manual selection of boot entry loaded by GRUB boot loader. This is useful for maintenance boot or to edit/modify boot entry  In rhel 7 default grub timeout is 5 second.

In rhel 7 /boot/grub directory is not present nor /boot/grub/menu.list. In rhel 7 grub is modified with grub2 and we can use /etc/default/grub file to modify boot loader configuration.

It’s not recommended to modify any grub file in rhel 7 apart from /etc/default/grub.

Following are the default values from /etc/default/grub file.

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