Category: linux

Will start learning RedHat Enterprise Linux 7 Installation in this post.

We have many new features in RHEL7 and simple differences in installation as well comparing to old version’s that we were given input like hostname, timezone, package selection, network configuration, kdump configuration, etc… in next next screen’s. But, in RHEL7 we can provide those details on a single screen. However all the remaining will be the same.

Using RHEL7 media boot the machine and you will receive a screen like below.

Now select “Install Red Hat Enterprise Linux 7.3” to begin the installation.

As first part, you will get a screen that is asking you to select the System language and keyboard layout like below.

Then next you will get a screen which is the place to provide all information to install the operating system.

In this screen, you can provide all the information like Software selection, Partitioning in Installation destination tab, time zone, etc…

Now, will edit some of the configuration based on our requirement.

As first, here editing time zone part and selecting Asia/ Kolkata like below.

you can select the time zone in two ways one is by clicking on India over the map and another one is selecting Asia and Kolkata in the drop-down list.

And, click on the done button which is showing the left corner of upper on the screen to complete this part.

Likewise, we should click on done for each and every part.

Now, Click on “Software selection” tab to select packages

Will continue with default one which is “minimal installation”.

Based on the selected packages group, it will install the required packages.

Next, Click on “Installation destination” to create partitions.

We have two option at this stage. One is “Automatically configure partitions” and another one is “I will configure partitioning”

If you select the first option, it will create the partition automatically with LVM and if you select the second option, we need to provide the partition details manually.

Here let us see how to create manual partitions.

Once you selected the second option, you will get a screen asking for partition type Standard, LVM, etc…

select on Standard one to create a normal partition.

and click done to go next screen of partition creation.

It will ask for the mount point with size like below. Below filesystem, creation is compulsory while doing manual partitioning.

1. boot – Contains bootloader and partition information
2. / (root)
3. swap – Virtual memory

Like above will create the three mandate partition to continue the installation.

and click done to go back to the main screen.

and it will ask our confirmation to write the partition changes on the disk. Click “Accept Changes”.

And now, click “Begin Installation” to start the package installation.

In package installation screen, we can see that password has not been set still. So, click on “Root Password” to set the root password. and click done.

See the screen after root password has been assigned.

Once installation completed, will ask for the reboot. Click on “Reboot” button to complete the installation.

We compeleted RHEL7 installation successfully.

 

 

 

 

 

In this post we are going to see : Limiting CPU and Memory usage to users/groups.

In large environments, there is a chance to access single system by more than one users at a time. So, user’s can access the resources highly.

For our exercise going to use RHEL7 Operating System.

CGroups will help us to limit the resources by group of users.

We have below users created already to do practise.

[root@server ~]# grep home /etc/passwd
lbcuser1:x:1005:1007::/home/lbcuser1:/bin/bash
lbcuser2:x:1006:1008::/home/lbcuser2:/bin/bash
lbcuser3:x:1007:1009::/home/lbcuser3:/bin/bash
lbcuser:x:1008:1011::/home/lbcuser:/bin/bash

Users are assigned to below mentioned groups.

Groups:    lbcgroup, finance, admin

[root@server ~]# grep "lbcuser" /etc/group
finance:x:1003:lbcuser2
lbcgroup:x:1010:lbcuser1,lbcuser
admin:x:1012:lbcuser3

To work on this, lbcgroup package should be installed and will use /etc/cgconfig.conf and /etc/cgrules.conf to apply the rules overs the users to limit the resources use.

follow the below steps to apply rules by per Group:

[root@server ~]# vi /etc/cgconfig.conf
mount {
 cpu = /cgroup/cpu_and_mem;
 cpuacct = /cgroup/cpu_and_mem;
 memory = /cgroup/cpu_and_mem;
}

group finance {
 cpu {
 cpu.shares="250";
 }
 cpuacct {
 cpuacct.usage="0";
 }
 memory {
 memory.limit_in_bytes="1G";
 memory.memsw.limit_in_bytes="2G";
 }
}

group lbcgroup {
 cpu {
 cpu.shares="250";
 }
 cpuacct {
 cpuacct.usage="0";
 }
 memory {
 memory.limit_in_bytes="1G";
 memory.memsw.limit_in_bytes="2G";
 }
}

group admin {
 cpu {
 cpu.shares="500";
 }
 cpuacct {
 cpuacct.usage="0";
 }
 memory {
 memory.limit_in_bytes="1G";
 memory.memsw.limit_in_bytes="2G";
 }
}

While starting the server, above configuration file will mount cpu, cpuacct and memory subsystems to a cpu_and _memory cgroup.

CPU:

cpu-shares parameter used to assign the the CPU resources which is available to each and every processes. Assigning parameter values as 250, 250 and 500 for finance, lbcgroup and admin groups in cgroup will split the CPU resources in 1:1:2 ratio. If only one process is running, it doesn’t matter in which cgroup it falls. CPU limitation will be applied, when there is more than one process running.

cpuacct:

cpuacct.usage=”0″ this value is used to reset the CPU usage on cpuacct.usage and cpuacct_percpu files. These files contains the total CPU utilized time by all the process.

Memory:

memory.limit_in_bytes=”1G” parameter says that how much memory allowed to use by a cgroup.

memory.memsw.limit_in_bytes=”2G” parameter says that how much swap space allowed to use by a cgroup

cgrulesengd:

Start this daemon using below command:

[root@server ~]# systemctl start cgred

This daemon will help to move process to specific cgroup and for that we need to configure /etc/cgrules.conf like below

[root@server ~]# vi /etc/cgrules.conf
# /etc/cgrules.conf
#The format of this file is described in cgrules.conf(5)
#manual page.

@finance  cpu,memory finance
@lbcgroup cpu,memory lbcgroup
@admin    cpu        admin

Like above will assign rules to group.

In this, process will be moved to cgroup based on which user started this process and belongs to which group.

For example, Process detects the limitations from lbcgroup cgroup, which is started by lbcuser1 user and it will move to /cgroup/cpu_and_mem/lbcgroup/tasks file.

cgconfig:

Start this daemon to create hierarchy of cgroup to set the required parameters  in all cgroups.

[root@server ~]# systemctl start cgconfig

and to make all changes persistent across reboot, configure both(cgred, cgconfig) services to be started by default.

[root@server ~]# systemctl enable cgred

[root@server ~]# systemctl enable cgconfig

 

Reference: Red Hat official documentation

In this post going to see How to install Graphical user Interface/GUI on RedHat Linux.

We have 7 run levels in RedHat and in that, runlevel 5 is used for GUI.

Use below command to change from current runlevel to GUI(before changing to graphical mode, make sure GNOME package installed):

[root@server ~]# init 5

To set GUI as default runlevel, use the below command and reboot the machine.

[root@server ~]# systemctl set-default graphical.target

If without any error runlevel switched to GUI, than package is already installed in your machine.

If you are receiving any error, than you should install the GNOME package.

Let’s see how to install the GUI in RedHat 7.

We will use yum package manager to install the GUI.

We have two types of repository that, one is online and another one is local repository.First decide which repository going to use to install GNOME package.

If you’re machine connected with internet, register in redhat repository using below command.

[root@server ~]# subscription-manager register
[root@server ~]# subscription-manager refresh
[root@server ~]# subscription-manager attach --auto

To use local repository make sure its already configured in your machine. Click here to know how to configure local yum repository.

Use the below command to check the group name for GNOME installation.

[root@server ~]# yum grouplist
Loaded plugins: product-id, search-disabled-repos, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use su bscription-manager to register.
There is no installed groups file.
Maybe run: yum groups mark convert (see man yum)
Available Environment Groups:
 Minimal Install
 Infrastructure Server
 File and Print Server
 Basic Web Server
 Virtualization Host
 Server with GUI
Available Groups:
 Compatibility Libraries
 Console Internet Tools
 Development Tools
 Graphical Administration Tools
 Legacy UNIX Compatibility
 Scientific Support
 Security Tools
 Smart Card Support
 System Administration Tools
 System Management
Done

We should install “Server with GUI” using yum like below.

[root@server ~]# yum -y groupinstall "Server with GUI"

Now successfully installed GUI in our machine. Try to switch using “init 5” command.

Thanks for reading this post.

Reference: Red Hat Discussion

In this post we are going to see(Permission handling in Linux) how to set permission for files and directories in linux/unix.

Before set/unset permission we should check the existing permission for a file usinf ll <filename> command like below.

[root@server ~]# ll abu
-rwxrwxrwx. 1 abu root 113 Dec 11 20:22 abu

We can assign permission based on below categories and same has been display while executing ll or ls –l command.

User:    u

Group:  g

Others:  o

Numeric values used for changing/identifying the permissions:

Read:       4, r

Write:      2, w

Execute:  1, x

Command used for changing file permission:

#Chmod 655 <filename>

Example:

Command to set permission:

We are going to set permission for file abu from 777 to 755 using below command. 755 will have full permission for user, read and execute for group and others.

[root@server ~]# chmod 755 abu
[root@server ~]# ll abu
-rwxr-xr-x. 1 abu root 113 Dec 11 20:22 abu

Also will set the permissions usings characters like below.

Read:        r

Write:       w

Execute:  x

Example:

Command to set permission using characters:

In the below example going to set execute permission alone to others

[root@server ~]# ll abu1
-rwxr-xr--. 1 root abu 0 Dec 11 20:17 abu1
[root@server ~]# chmod o+x abu1
[root@server ~]# ll abu1
-rwxr-xr-x. 1 root abu 0 Dec 11 20:17 abu1

Changing ownership of a file or directory:

#Chwon user:group <filename>

example:

In below example going to change owner of the directory as lbcuser for lbc directory. User has been created already.

Note: Existing owner and group will be root.

before changing owhership:

[root@server ~]# mkdir lbc
[root@server ~]# ll | grep lbc
drwxr-xr-x. 2 root root 6 Dec 16 20:33 lbc

after changing ownership:

[root@server ~]# chown lbcuser lbc
[root@server ~]# ll | grep lbc
drwxr-xr-x. 2 lbcuser root 6 Dec 16 20:33 lbc

using chown command will change group as well like below.

Going to change group as finance.

[root@server ~]# chown :finance lbc
[root@server ~]# ll | grep lbc
drwxr-xr-x. 2 lbcuser finance 6 Dec 16 20:33 lbc

Will change the group alone using chgrp command:

[root@server ~]# mkdir lbc1
[root@server ~]# chgrp finance lbc1
[root@server ~]# ll | grep lbc1
drwxr-xr-x. 2 root finance 6 Dec 16 20:47 lbc1

 

Reference: RedHat Document

In this post we are going to securing files and directories using ACL in RHEL7/Cent OS 7.

In this post we are going to see how to secure files and directories using ACL.

As first step need to check kernel compatibility for ACL using below command.

[root@server ~]# grep -i acl /boot/config*
CONFIG_EXT4_FS_POSIX_ACL=y
CONFIG_XFS_POSIX_ACL=y
CONFIG_BTRFS_FS_POSIX_ACL=y
CONFIG_FS_POSIX_ACL=y
CONFIG_GENERIC_ACL=y
CONFIG_TMPFS_POSIX_ACL=y
CONFIG_NFS_V3_ACL=y
CONFIG_NFSD_V2_ACL=y
CONFIG_NFSD_V3_ACL=y
CONFIG_NFS_ACL_SUPPORT=m
CONFIG_CEPH_FS_POSIX_ACL=y
CONFIG_CIFS_ACL=y

Above output will says that this kernel is compatible with ACL access since we could see all are marked as yes POSIX_ACL=y. 

If it is set as N. Than we need to rebuild the kernel.

Next need to install the packages.

Required packages for ACL:

acl

nfs4-acl-tools

libacl

Now install all the above three packages using yum:

Link to see how to configure yum locally click here

[root@server ~]# yum -y install nfs4-acl* acl libacl

Will assign read, write and execute permission to files and directories using ACL and will mention characters ugo/rwx  in commands for permissions respectively.

Now will see a example which will help us to understand clearly.

Create three users and one group respectively like below.

[root@server ~]# useradd lbcuser1
[root@server ~]# useradd lbcuser2
[root@server ~]# useradd lbcuser3
[root@server ~]# groupadd lbcgroup
[root@server ~]# passwd lbcuser1
Changing password for user lbcuser1.
New password:
BAD PASSWORD: The password is a palindrome
Retype new password:
passwd: all authentication tokens updated successfully.

Above screen password has been generated for only lbcuser1.Same like that need to set password for other 2 users.

Now add the lbcgroup group as secondry group for lbcuser1 and lbcuser2 users.

[root@server ~]# usermod -aG lbcgroup lbcuser1
[root@server ~]# usermod -aG lbcgroup lbcuser2

Create a directory and a file inside of that directory to assign and check permissions using acl.

[root@server ~]# mkdir /tmp/data
[root@server ~]# touch /tmp/data/testfile.txt

Now change the group as lbcgroup to the file like below.

[root@server ~]# chown :lbcgroup /tmp/data/testfile.txt
[root@server ~]# ll /tmp/data/testfile.txt
-rw-r--r--. 1 root lbcgroup 0 Dec 15 21:14 /tmp/data/testfile.txt

set the permission 770 using chmod command to the testfile.txt.

Now we can login as lbcuser1 and lbcuser2 and than will try to insert content in testfile.txt.

Sure both users can able to insert content in the file. Because, both users and files group is same(lbcgroup).

[root@server ~]# su lbcuser1
[lbcuser1@server root]$ echo "My name is lbcuser1..." > /tmp/data/testfile.txt
[lbcuser1@server root]$ exit
exit
[root@server ~]# su lbcuser2
[lbcuser2@server root]$ echo "My name is lbcuser2..." > /tmp/data/testfile.txt
[lbcuser2@server root]$ exit
exit
[root@server ~]#

and now will try to insert content as lbcuser3. It will give error. Since, its not the owner and member of lbcgroup for that file.

[root@server ~]# su lbcuser3
[lbcuser3@server root]$ echo "My name is lbcuser3..." > /tmp/data/testfile.txt
bash: /tmp/data/testfile.txt: Permission denied

So, now will provide read and write permission using ACL without adding the lbcuser3 in lbcgroup and will check it again to insert content into the file.

[root@server ~]# setfacl -R -m u:lbcuser3:rw /tmp/data/testfile.txt
[root@server ~]# su lbcuser3
[lbcuser3@server root]$ echo "My name is lbcuser3..." > /tmp/data/testfile.txt
[lbcuser3@server root]$ cat /tmp/data/testfile.txt
My name is lbcuser3...

Since we user single > symbol to redirect the echo command out into the file, its showing our last content which is “My name is lbcuser3…”

To set permission for group will use g in above command where we used u and groupname where we given username like below.

[root@server ~]# setfacl -R -m g:lbcgroup:rw /tmp/data/testfile.txt

To check the existing ACL permission of a file use getfacl command.

[root@server ~]# getfacl /tmp/data/testfile.txt
getfacl: Removing leading '/' from absolute path names
# file: tmp/data/testfile.txt
# owner: root
# group: lbcgroup
user::rwx
user:lbcuser3:rw-
group::rwx
mask::rwx
other::---

Same like file will set permission to directory as well.

Command to set permission for directory:

below command will help us to set read permission alone for other users which is not owner/group of the directory.

[root@server ~]# setfacl -m d:o:r /tmp/data
[root@server ~]# getfacl /tmp/data
getfacl: Removing leading '/' from absolute path names
# file: tmp/data
# owner: root
# group: root
user::rwx
group::r-x
other::r-x
default:user::rwx
default:group::r-x
default:other::r--