How to print the epoch using date command

To print epoch - The seconds that has passed since 1970-01-01 00:00:00 UTC, run the following command,

date +"%s" 1480572641

Here %s tells date to print the epoch.

Tested on: CentOS 7, Debian 8, Ubuntu 16.04

How to find what package provides a specific file on RHEL, CentOS, Fedora

In your system administration life time, suppose you're looking forward to edit a configuration file and it turns out that the file is not available. You forgot what package to install to have that file or what package contains that file. What would you do then? To get the answer, read this post.

To find out which package in the repository contains a specific file, you can use the repoquery command. The syntax to do that is,

repoquery -qf file_path

Here file_path is the file that you're looking for.

Example: Find the package that is associated with a specific file /etc/my.cnf

To check what package provides the file /etc/my.cnf, run the following command.

repoquery -qf /etc/my.cnf

mariadb-libs-1:5.5.44-2.el7.centos.x86_64
mariadb-libs-1:5.5.44-2.el7.centos.i686

From the output, we can see that the packages that provides the specific file /etc/my.cnf is mariadb-libs.

Tested on: CentOS 7

How to find what configuration files are associated with a specific installed package using rpm

To check what configuration files are associated with a specific package that is already installed on your system using rpm command, use the syntax as written below.

rpm -qc package_name

Here package_name is any package that is already installed on your system.

Example: Find the associated configuration files of Apache HTTP server

To check the configuration files that are associated with the package httpd, the Apache HTTP server, run the following command.

rpm -qc httpd

/etc/httpd/conf.d/autoindex.conf
/etc/httpd/conf.d/userdir.conf
/etc/httpd/conf.d/welcome.conf
/etc/httpd/conf.modules.d/00-base.conf
/etc/httpd/conf.modules.d/00-dav.conf
/etc/httpd/conf.modules.d/00-lua.conf
/etc/httpd/conf.modules.d/00-mpm.conf
/etc/httpd/conf.modules.d/00-proxy.conf
/etc/httpd/conf.modules.d/00-systemd.conf
/etc/httpd/conf.modules.d/01-cgi.conf
/etc/httpd/conf/httpd.conf
/etc/httpd/conf/magic
/etc/logrotate.d/httpd
/etc/sysconfig/htcacheclean
/etc/sysconfig/httpd

Tested on: CentOS 7

How to Find Which Package Contains a Specific File Using rpm Command

At times you need to know which package contains a specific file on rpm based Linux distros such as Fedora, RedHat(RHEL), CentOS, openSUSE, SLE etc. Read below to learn how.

Let's say you want to know what package provides the ip command. It's a two step process.

Finding the location of the ip binary:

To find the ip binary location, run the following command.

which ip /sbin/ip

The location is /sbin/ip as it's seen from the output of 'which'.

Finding the package name with rpm:

To find the package that contains the binary /sbin/ip, run the following command.

rpm -qf /sbin/ip iproute-3.10.0-54.el7.x86_64

From the output of 'rpm' command, you can see that the package is "iproute-3.10.0-54.el7.x86_64". So this is the package that we were looking for.

You can use any file path with 'rpm -qf' command. As long as the rpm database knows about the file. You will get a result.

Tested on: CentOS 7

Find the UUID of your network interface or connection

Today I was looking at the /etc/sysconfig/network-scripts/ifcfg-enp0s3 file and I came across the line that says UUID. I was thinking what is UUID of a network interface? Then I started thinking about how to find UUIDs of network interfcaes. I looked on the internet but I got no solution. Then I thought of trying to find it myself using network management commands. I did find a solution.

To find the UUIDs of your network connection, run the following command.

nmcli connection show

NAME                UUID                                  TYPE            DEVICE 
virbr0              4e02750f-13d9-4662-bfc2-10f9ae1a71bd  bridge          virbr0 
Wired connection 1  09066de3-7eb7-4ee1-9059-c651b6dff7a6  802-3-ethernet  --     
enp0s3              5144084b-0537-4e4b-9f15-065431bc6d38  802-3-ethernet  --  

From the output of this command, you can find the UUID of a connection on CentOS, Fedora, RedHat(RHEL), Ubuntu, Debian operating systems.

Tested on: CentOS 7, Ubuntu 16.04 LTS

Mount iscsi Network Devices using /etc/fstab

If you're trying to mount network devices automatically at boot on Linux and your system is not booting correctly. This post is for you.

Today I was working with iscsi. I created portals, acls, luns, targets with targetcli. But when I tried to mount it automatically through fstab file on boot, my system wasn't booting. I looked online and I found that I had to change the mount option. I did and it worked. I am going to write what mount option I used in this post.

When my system wasn't booting, my /etc/fstab configuration file looked like this,

#
# /etc/fstab
# Created by anaconda on Thu Nov 24 03:07:55 2016
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
/dev/mapper/centos-root /                       xfs     defaults        0 0
UUID=0d83fc00-ee94-4741-8163-717418187f59 /boot                   xfs     defaults        0 0
/dev/mapper/centos-swap swap                    swap    defaults        0 0
UUID=f246ba49-5772-4efc-bec2-28ff76f46f79 /root/mounts/sdb xfs defaults 0 0

Here UUID=f246ba49-5772-4efc-bec2-28ff76f46f79, this is the iscsi drive I was trying to mount. The mount option was "defaults". But to get it to work, I had to change the mount option to "_netdev". What this option does it, it attempts to mount this device after all the network connection is initialized.

So my working configuration looked like this,

#
# /etc/fstab
# Created by anaconda on Thu Nov 24 03:07:55 2016
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
/dev/mapper/centos-root /                       xfs     defaults        0 0
UUID=0d83fc00-ee94-4741-8163-717418187f59 /boot                   xfs     defaults        0 0
/dev/mapper/centos-swap swap                    swap    defaults        0 0
UUID=f246ba49-5772-4efc-bec2-28ff76f46f79 /root/mounts/sdb xfs _netdev  0 0

Tested on: CentOS 7

How to Open TCP and UDP ports using firewall-cmd on CentOS/RedHat/Fedora

This post is about how to open specific tcp and udp ports using the command firewall-cmd. So without further due, let's get started.

Opening TCP ports:

Let's say, I want to open the tcp ports 80 and 443 which are used by http and https protocol respectively.

To do that, run the following commands,

firewall-cmd --permanent --add-port=80/tcp
firewall-cmd --permanent --add-port=443/tcp

Opening UDP ports:

Let's say, I want to open the udp port 53, which is used by bind dns service.

To do that, run the following command,

firewall-cmd --permanent --add-port=53/udp

Reload the Configuration:

Now we have to reload firewall-cmd configurations. To do that, run the following command,

firewall-cmd --reload

Verification:

To verify that the commands worked, let's view the current opened port list,

firewall-cmd --list-ports 443/tcp 80/tcp 53/udp

Tested on: CentOS 7