How to Setup Local HTTP Yum Repository on CentOS 7

A software repository (“repo” in short) is a central file storage location to keep and maintain software packages, from which users can retrieve packages and install on their computers.

Repositories are often stored on servers on a network for example the internet, which can be accessed by multiple users. However, you can create and configure a local repository on your computer and access it as a single user or allow access to other machines on your LAN (Local Area Network).

One advantage of a setting up a local repository is that you don’t need internet connection to install sofware packages.

YUM (Yellowdog Updater Modified) is a widely used package management tool for RPM (RedHat Package Manager) based Linux systems, which makes sofware installation easy on Red Hat/CentOS Linux.

In this article, we will explain how to setup a local YUM repository over HTTP (Nginx) web server on CentOS 7 VPS and also show you how to find and install software packages on client CentOS 7 machines.

Our Testing Environment

Yum HTTP Repository Server: CentOS 7 [192.168.0.100]
Client Machine:  CentOS 7 [192.168.0.101]

Step 1: Install Nginx Web Server

1. First start by installing Nginx HTTP server from the EPEL repository using the YUM package manager as follows.

# yum install epel-release
# yum install nginx 

2. Once you have installed Nginx web server, you can start it for the first time and enable it to start automatically at system boot.

 
# systemctl start nginx
# systemctl enable nginx
# systemctl status nginx

3. Next, you need to open port 80 and 443 to allow web traffic to Nginx service, update the system firewall rules to permit inbound packets on HTTP and HTTPS using the commands below.

# firewall-cmd --zone=public --permanent --add-service=http
# firewall-cmd --zone=public --permanent --add-service=https
# firewall-cmd --reload

4. Now you can confirm that your Nginx server is up and running, using the following URL; if you see the default Nginx web page, all is well.

http://SERVER_DOMAIN_NAME_OR_IP 

Nginx Default Page

Step 2: Create Yum Local Repository

5. In this step, you need to install the required packages for creating, configuring and managing your local repository.

# yum install createrepo  yum-utils

6. Next, create the necessary directories (yum repositories) that will store packages and any related information.

# mkdir -p /var/www/html/repos/{base,centosplus,extras,updates}

7. Then use the reposync tool to synchronize CentOS YUM repositories to the local directories as shown.

# reposync -g -l -d -m --repoid=base --newest-only --download-metadata --download_path=/var/www/html/repos/
# reposync -g -l -d -m --repoid=centosplus --newest-only --download-metadata --download_path=/var/www/html/repos/
# reposync -g -l -d -m --repoid=extras --newest-only --download-metadata --download_path=/var/www/html/repos/
# reposync -g -l -d -m --repoid=updates --newest-only --download-metadata --download_path=/var/www/html/repos/

Sample Output

Loaded plugins: fastestmirror, langpacks
Loading mirror speeds from cached hostfile
 * base: mirrors.fibergrid.in
 * epel: mirror.xeonbd.com
 * extras: mirrors.fibergrid.in
 * updates: mirrors.fibergrid.in
base/7/x86_64/group                                                    | 891 kB  00:00:02     
No Presto metadata available for base
(1/9911): 389-ds-base-snmp-1.3.7.5-18.el7.x86_64.rpm                   | 163 kB  00:00:02     
(2/9911): 389-ds-base-devel-1.3.7.5-18.el7.x86_64.rpm                  | 267 kB  00:00:02     
(3/9911): ElectricFence-2.2.2-39.el7.i686.rpm                          |  35 kB  00:00:00     
(4/9911): ElectricFence-2.2.2-39.el7.x86_64.rpm                        |  35 kB  00:00:00     
(5/9911): 389-ds-base-libs-1.3.7.5-18.el7.x86_64.rpm                   | 695 kB  00:00:04     
(6/9911): GConf2-devel-3.2.6-8.el7.i686.rpm                            | 110 kB  00:00:00     
(7/9911): GConf2-devel-3.2.6-8.el7.x86_64.rpm                          | 110 kB  00:00:00     
(8/9911): GConf2-3.2.6-8.el7.i686.rpm                                  | 1.0 MB  00:00:06     

In the above commands, the option:

• -g – enables removing of packages that fail GPG signature checking after downloading.
• -l – enables yum plugin support.
• -d – enables deleting of local packages no longer present in repository.
• -m – enables downloading of comps.xml files.
• --repoid – specifies the repository ID.
• --newest-only – tell reposync to only pull the latest version of each package in the repos.
• --download-metadata – enables downloading all the non-default metadata.
• --download_path – specifies the path to download packages.

8. Next, check the contents of your local directories to ensure that all the packages have been synchronized locally.

# ls -l /var/www/html/repos/base/
# ls -l /var/www/html/repos/base/Packages/
# ls -l /var/www/html/repos/centosplus/
# ls -l /var/www/html/repos/centosplus/Packages/
# ls -l /var/www/html/repos/extras/
# ls -l /var/www/html/repos/extras/Packages/
# ls -l /var/www/html/repos/updates/
# ls -l /var/www/html/repos/updates/Packages/

9. Now create a new repodata for the local repositories by running the following commands, where the flag -g is used to update the package group information using the specified .xml file.

# createrepo -g comps.xml /var/www/html/repos/base/  
# createrepo -g comps.xml /var/www/html/repos/centosplus/ 
# createrepo -g comps.xml /var/www/html/repos/extras/  
# createrepo -g comps.xml /var/www/html/repos/updates/  

10. To enable viewing of repositories and packages in them, via a web browser, create a Nginx server block which points to the root of your repositories as shown.

# vim /etc/nginx/conf.d/repos.conf 

Add the following configuration ot file repos.conf.

server {
        listen   80;
        server_name  repos.test.lab; #change  test.lab to your real domain 
        root   /var/www/html/repos;
        location / {
                index  index.php index.html index.htm;
                autoindex on; #enable listing of directory index
        }
}

Save the file and close it.

11. Then restart your Nginx server and view the repositories from a web browser using the following URL.

http://repos.test.lab

View Local Yum Repositories

Step 3: Create Cron Job to Synchronize and Create Repositories

12. Next, add a cron job that will automatically synchronize your local repos with the official CentOS repos to grab the updates and security patches.

# vim /etc/cron.daily/update-localrepos

Add these commands in the script.

#!/bin/bash
##specify all local repositories in a single variable
LOCAL_REPOS=”base centosplus extras updates”
##a loop to update repos one at a time 
for REPO in ${LOCAL_REPOS}; do
reposync -g -l -d -m --repoid=$REPO --newest-only --download-metadata --download_path=/var/www/html/repos/
createrepo -g comps.xml /var/www/html/repos/$REPO/  
done

Save the script and close it and set the appropriate permissions on it.

# chmod 755 /etc/cron.daily/update-localrepos

Step 4: Setup Local Yum Repository on Client Machines

13. Now on your CentOS client machines, add your local repos to the YUM configuration.

# vim /etc/yum.repos.d/local-repos.repo

Copy and paste the configuration below in the file local-repos.repo (make changes where necessary).

[local-base]
name=CentOS Base
baseurl=http://repos.test.lab/base/
gpgcheck=0
enabled=1

[local-centosplus]
name=CentOS CentOSPlus
baseurl=http://repos.test.lab/centosplus/
gpgcheck=0
enabled=1

[local-extras]
name=CentOS Extras
baseurl=http://repos.test.lab/extras/
gpgcheck=0
enabled=1

[local-updates]
name=CentOS Updates
baseurl=http://repos.test.lab/updates/
gpgcheck=0
enabled=1

Save the file and start using your local YUM mirrors.

14. Next, run the following command to view your local repos in the list of available YUM repos, on the client machines.

#  yum repolist
OR
# yum repolist all

View Local Yum Repositories on Client

That’s all! In this article, we have explained how to setup a local YUM repository on CentOS 7. We hope that you found this guide useful. If you have any questions, or any other thoughts to share, use the comment form below.

20 Linux YUM (Yellowdog Updater, Modified) Commands for Package Management

In this article, we will learn how to install, update, remove, find packages, manage packages and repositories on Linux systems using YUM (Yellowdog Updater Modified) tool developed by RedHat. The example commands shown in this article are practically tested on our CentOS 6.3 server, you can use these material for study purpose, certifications or just to explore ways to install new packages and keep your system up-to-date. The basic requirement of this article is, you must have a basic understanding of commands and a working Linux operating system, where you can explore and practice all the commands listed below.

20 Linux Yum Commands

What is YUM?

YUM (Yellowdog Updater Modified) is an open source command-line as well as graphical based package management tool for RPM (RedHat Package Manager) based Linux systems. It allows users and system administrator to easily install, update, remove or search software packages on a systems. It was developed and released by Seth Vidal under GPL (General Public License) as an open source, means anyone can be allowed to download and access the code to fix bugs and develop customized packages. YUM uses numerous third party repositories to install packages automatically by resolving their dependencies issues.

1. Install a Package with YUM

To install a package called Firefox 14, just run the below command it will automatically find and install all required dependencies for Firefox.

# yum install firefox
Loaded plugins: fastestmirror
Dependencies Resolved

================================================================================================
 Package                    Arch        Version                    Repository            Size        
================================================================================================
Updating:
firefox                        i686        10.0.6-1.el6.centos     updates             20 M
Updating for dependencies:
 xulrunner                     i686        10.0.6-1.el6.centos     updates             12 M

Transaction Summary
================================================================================================
Install       0 Package(s)
Upgrade       2 Package(s)

Total download size: 32 M
Is this ok [y/N]: y
Downloading Packages:
(1/2): firefox-10.0.6-1.el6.centos.i686.rpm                                |  20 MB   01:10
(2/2): xulrunner-10.0.6-1.el6.centos.i686.rpm                              |  12 MB   00:52
------------------------------------------------------------------------------------------------
Total                                                           63 kB/s |  32 MB   02:04

Updated:
  firefox.i686 0:10.0.6-1.el6.centos

Dependency Updated:
  xulrunner.i686 0:10.0.6-1.el6.centos

Complete!

The above command will ask confirmation before installing any package on your system. If you want to install packages automatically without asking any confirmation, use option -y as shown in below example.

# yum -y install firefox

2. Removing a Package with YUM

To remove a package completely with their all dependencies, just run the following command as shown below.

# yum remove firefox
Loaded plugins: fastestmirror
Setting up Remove Process
Resolving Dependencies
--> Running transaction check
---> Package firefox.i686 0:10.0.6-1.el6.centos set to be erased
--> Finished Dependency Resolution

Dependencies Resolved

====================================================================================================
 Package                    Arch        Version                        Repository            Size        
====================================================================================================
Removing:
 firefox                    i686        10.0.6-1.el6.centos            @updates              23 M

Transaction Summary
====================================================================================================
Remove        1 Package(s)
Reinstall     0 Package(s)
Downgrade     0 Package(s)

Is this ok [y/N]: y
Downloading Packages:
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
  Erasing        : firefox-10.0.6-1.el6.centos.i686                                                                                                                          1/1

Removed:
  firefox.i686 0:10.0.6-1.el6.centos

Complete!

Same way the above command will ask confirmation before removing a package. To disable confirmation prompt just add option -y as shown in below.

# yum -y remove firefox

3. Updating a Package using YUM

Let’s say you have outdated version of MySQL package and you want to update it to the latest stable version. Just run the following command it will automatically resolve all dependencies issues and install them.

# yum update mysql
Loaded plugins: fastestmirror
Dependencies Resolved

============================================================================================================
 Package            Arch                Version                    Repository                    Size
============================================================================================================
Updating:
 vsftpd             i386                2.0.5-24.el5_8.1           updates                       144 k

Transaction Summary
============================================================================================================
Install       0 Package(s)
Upgrade       1 Package(s)

Total size: 144 k
Is this ok [y/N]: y
Downloading Packages:
Running rpm_check_debug
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
  Updating       : vsftpd                                                                     1/2
  Cleanup        : vsftpd                                                                     2/2

Updated:
  vsftpd.i386 0:2.0.5-24.el5_8.1

Complete!

4. List a Package using YUM

Use the list function to search for the specific package with name. For example to search for a package called openssh, use the command.

# yum list openssh
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirror.neu.edu.cn
 * epel: mirror.neu.edu.cn
 * extras: mirror.neu.edu.cn
 * rpmforge: mirror.nl.leaseweb.net
 * updates: mirror.nus.edu.sg
Installed Packages
openssh.i386                                       4.3p2-72.el5_6.3                                                                      installed
Available Packages                                 4.3p2-82.el5                                                                          base

To make your search more accurate, define package name with their version, in case you know. For example to search for a specific version openssh-4.3p2 of the package, use the command.

# yum list openssh-4.3p2

5. Search for a Package using YUM

If you don’t remember the exact name of the package, then use search function to search all the available packages to match the name of the package you specified. For example, to search all the packages that matches the word .

# yum search vsftpd
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirror.neu.edu.cn
 * epel: mirror.neu.edu.cn
 * extras: mirror.neu.edu.cn
 * rpmforge: mirror.nl.leaseweb.net
 * updates: ftp.iitm.ac.in
============================== Matched: vsftpd ========================
ccze.i386 : A robust log colorizer
pure-ftpd-selinux.i386 : SELinux support for Pure-FTPD
vsftpd.i386 : vsftpd - Very Secure Ftp Daemon

6. Get Information of a Package using YUM

Say you would like to know information of a package before installing it. To get information of a package just issue the below command.

# yum info firefox
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirror.neu.edu.cn
 * epel: mirror.neu.edu.cn
 * extras: mirror.neu.edu.cn
 * rpmforge: mirror.nl.leaseweb.net
 * updates: ftp.iitm.ac.in
Available Packages
Name       : firefox
Arch       : i386
Version    : 10.0.6
Release    : 1.el5.centos
Size       : 20 M
Repo       : updates
Summary    : Mozilla Firefox Web browser
URL        : http://www.mozilla.org/projects/firefox/
License    : MPLv1.1 or GPLv2+ or LGPLv2+
Description: Mozilla Firefox is an open-source web browser, designed for standards
           : compliance, performance and portability.

7. List all Available Packages using YUM

To list all the available packages in the Yum database, use the below command.

# yum list | less

8. List all Installed Packages using YUM

To list all the installed packages on a system, just issue below command, it will display all the installed packages.

# yum list installed | less

9. Yum Provides Function

Yum provides function is used to find which package a specific file belongs to. For example, if you would like to know the name of the package that has the /etc/httpd/conf/httpd.conf.

# yum provides /etc/httpd/conf/httpd.conf
Loaded plugins: fastestmirror
httpd-2.2.3-63.el5.centos.i386 : Apache HTTP Server
Repo        : base
Matched from:
Filename    : /etc/httpd/conf/httpd.conf

httpd-2.2.3-63.el5.centos.1.i386 : Apache HTTP Server
Repo        : updates
Matched from:
Filename    : /etc/httpd/conf/httpd.conf

httpd-2.2.3-65.el5.centos.i386 : Apache HTTP Server
Repo        : updates
Matched from:
Filename    : /etc/httpd/conf/httpd.conf

httpd-2.2.3-53.el5.centos.1.i386 : Apache HTTP Server
Repo        : installed
Matched from:
Other       : Provides-match: /etc/httpd/conf/httpd.conf

10. Check for Available Updates using Yum

To find how many of installed packages on your system have updates available, to check use the following command.

# yum check-update

11. Update System using Yum

To keep your system up-to-date with all security and binary package updates, run the following command. It will install all latest patches and security updates to your system.

# yum update

12. List all available Group Packages

In Linux, number of packages are bundled to particular group. Instead of installing individual packages with yum, you can install particular group that will install all the related packages that belongs to the group. For example to list all the available groups, just issue following command.

# yum grouplist
Installed Groups:
   Administration Tools
   DNS Name Server
   Dialup Networking Support
   Editors
   Engineering and Scientific
   FTP Server
   Graphics
   Java Development
   Legacy Network Server
Available Groups:
   Authoring and Publishing
   Base
   Beagle
   Cluster Storage
   Clustering
   Development Libraries
   Development Tools
   Eclipse
   Educational Software
   KDE (K Desktop Environment)
   KDE Software Development

13. Install a Group Packages

To install a particular package group, we use option as groupinstall. Fore example, to install “MySQL Database“, just execute the below command.

# yum groupinstall 'MySQL Database'
Dependencies Resolved

=================================================================================================
Package        Arch      Version    Repository        Size
=================================================================================================
Updating:
 unixODBC                           i386      2.2.11-10.el5      base              290 k
Installing for dependencies:
 unixODBC-libs                      i386      2.2.11-10.el5      base              551 k

Transaction Summary
=================================================================================================
Install       1 Package(s)
Upgrade       1 Package(s)

Total size: 841 k
Is this ok [y/N]: y
Downloading Packages:
Running rpm_check_debug
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
  Installing     : unixODBC-libs 1/3
  Updating       : unixODBC         2/3
  Cleanup        : unixODBC         3/3

Dependency Installed:
  unixODBC-libs.i386 0:2.2.11-10.el5

Updated:
  unixODBC.i386 0:2.2.11-10.el5

Complete!

14. Update a Group Packages

To update any existing installed group packages, just run the following command as shown below.

# yum groupupdate 'DNS Name Server'

Dependencies Resolved
================================================================================================================
 Package   Arch         Version    Repository           Size
================================================================================================================
Updating:
 bind                           i386            30:9.3.6-20.P1.el5_8.2          updates              981 k
 bind-chroot                    i386            30:9.3.6-20.P1.el5_8.2          updates              47 k
Updating for dependencies:
 bind-libs                      i386            30:9.3.6-20.P1.el5_8.2          updates              864 k
 bind-utils                     i386            30:9.3.6-20.P1.el5_8.2          updates              174 k

Transaction Summary
================================================================================================================
Install       0 Package(s)
Upgrade       4 Package(s)

Total size: 2.0 M
Is this ok [y/N]: y
Downloading Packages:
Running rpm_check_debug
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
  Updating       : bind-libs            1/8
  Updating       : bind                 2/8
  Updating       : bind-chroot          3/8
  Updating       : bind-utils           4/8
  Cleanup        : bind                 5/8
  Cleanup        : bind-chroot          6/8
  Cleanup        : bind-utils           7/8
  Cleanup        : bind-libs            8/8

Updated:
  bind.i386 30:9.3.6-20.P1.el5_8.2                  bind-chroot.i386 30:9.3.6-20.P1.el5_8.2

Dependency Updated:
  bind-libs.i386 30:9.3.6-20.P1.el5_8.2             bind-utils.i386 30:9.3.6-20.P1.el5_8.2

Complete!

15. Remove a Group Packages

To delete or remove any existing installed group from the system, just use below command.

# yum groupremove 'DNS Name Server'

Dependencies Resolved

===========================================================================================================
 Package                Arch              Version                         Repository          Size
===========================================================================================================
Removing:
 bind                   i386              30:9.3.6-20.P1.el5_8.2          installed           2.1 M
 bind-chroot            i386              30:9.3.6-20.P1.el5_8.2          installed           0.0

Transaction Summary
===========================================================================================================
Remove        2 Package(s)
Reinstall     0 Package(s)
Downgrade     0 Package(s)

Is this ok [y/N]: y
Downloading Packages:
Running rpm_check_debug
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
  Erasing        : bind                                                   1/2
warning: /etc/sysconfig/named saved as /etc/sysconfig/named.rpmsave
  Erasing        : bind-chroot                                            2/2

Removed:
  bind.i386 30:9.3.6-20.P1.el5_8.2                                        bind-chroot.i386 30:9.3.6-20.P1.el5_8.2

Complete!

16. List Enabled Yum Repositories

To list all enabled Yum repositories in your system, use following option.

# yum repolist

repo id                     repo name                                            status
base                        CentOS-5 - Base                                      enabled:  2,725
epel                        Extra Packages for Enterprise Linux 5 - i386         enabled:  5,783
extras                      CentOS-5 - Extras                                    enabled:    282
mod-pagespeed               mod-pagespeed                                        enabled:      1
rpmforge                    RHEL 5 - RPMforge.net - dag                          enabled: 11,290
updates                     CentOS-5 - Updates                                   enabled:    743
repolist: 20,824

16. List all Enabled and Disabled Yum Repositories

The following command will display all enabled and disabled yum repositories on the system.

# yum repolist all

repo id                     repo name                                            status
C5.0-base                   CentOS-5.0 - Base                                    disabled
C5.0-centosplus             CentOS-5.0 - Plus                                    disabled
C5.0-extras                 CentOS-5.0 - Extras                                  disabled
base                        CentOS-5 - Base                                      enabled:  2,725
epel                        Extra Packages for Enterprise Linux 5 - i386         enabled:  5,783
extras                      CentOS-5 - Extras                                    enabled:    282
repolist: 20,824

17. Install a Package from Specific Repository

To install a particular package from a specific enabled or disabled repository, you must use –enablerepo option in your yum command. For example to Install PhpMyAdmin 3.5.2 package, just execute the command.

# yum --enablerepo=epel install phpmyadmin

Dependencies Resolved
=============================================================================================
 Package                Arch           Version            Repository           Size
=============================================================================================
Installing:
 phpMyAdmin             noarch         3.5.1-1.el6        epel                 4.2 M

Transaction Summary
=============================================================================================
Install       1 Package(s)

Total download size: 4.2 M
Installed size: 17 M
Is this ok [y/N]: y
Downloading Packages:
phpMyAdmin-3.5.1-1.el6.noarch.rpm                       | 4.2 MB     00:25
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
  Installing : phpMyAdmin-3.5.1-1.el6.noarch             1/1
  Verifying  : phpMyAdmin-3.5.1-1.el6.noarch             1/1

Installed:
  phpMyAdmin.noarch 0:3.5.1-1.el6

Complete!

18. Interactive Yum Shell

Yum utility provides a custom shell where you can execute multiple commands.

# yum shell
Loaded plugins: fastestmirror
Setting up Yum Shell
> update httpd
Loading mirror speeds from cached hostfile
 * base: mirrors.sin3.sg.voxel.net
 * epel: ftp.riken.jp
 * extras: mirrors.sin3.sg.voxel.net
 * updates: mirrors.sin3.sg.voxel.net
Setting up Update Process
>

19. Clean Yum Cache

By default yum keeps all the repository enabled package data in /var/cache/yum/ with each sub-directory, to clean all cached files from enabled repository, you need to run the following command regularly to clean up all the cache and make sure that there is nothing unnecessary space is using. We don’t want to give the output of the below command, because we like to keep cached data as it is.

# yum clean all

20. View History of Yum

To view all the past transactions of yum command, just use the following command.

# yum history

Loaded plugins: fastestmirror
ID     | Login user               | Date and time    | Action(s)      | Altered
-------------------------------------------------------------------------------
    10 | root               | 2012-08-11 15:19 | Install        |    3
     9 | root               | 2012-08-11 15:11 | Install        |    1
     8 | root               | 2012-08-11 15:10 | Erase          |    1 EE
     7 | root               | 2012-08-10 17:44 | Install        |    1
     6 | root               | 2012-08-10 12:19 | Install        |    2
     5 | root               | 2012-08-10 12:14 | Install        |    3
     4 | root               | 2012-08-10 12:12 | I, U           |   13 E<
     3 | root               | 2012-08-09 13:01 | Install        |    1 >
     2 | root               | 2012-08-08 20:13 | I, U           |  292 EE
     1 | System            | 2012-08-08 17:15 | Install        |  560
history list

How to run a command that requires sudo via SSH

With SSH you can run commands on remote machines, even if the command requires sudo privileges.

Secure Shell includes a lot of tricks, many of which can make your admin's life exponentially easier. One such trick is the ability to run commands on remote servers, without logging in. 

Sure, you can take the time to log into the server, run the command, and log out, but why not just do it all in one fell swoop? Not only is this handy, it's quite easy.

What you need

The only things you need for this is two more Linux machines, all of which include the openssh-server up and running (and accepting connections). If you don't have the SSH daemon installed, you can do this from the standard repositories. For instance, on the Ubuntu Server platform, the command to install the SSH daemon is:

sudo apt-get install openssh-server -y

For CentOS 7, the command is:

sudo yum install -y openssh-server

Once installed, you'll want to enable the server with the commands:
sudo systemctl start sshd
sudo systemctl enable sshd

Now that you have the SSH daemon running on your remote servers, you can send commands to them. Let's find out how.

Running a basic command

Let's get a listing of files on a remote /etc directory. To do this, the command is:
ssh USER@SERVER_IP "ls /etc"

Where USER is a remote user name, and SERVER_IP is the IP address of the remote server. Once you successfully enter the remote user's password, you will get a listing of the /etc/ directory on the remote server.

Easy peasy.

Running a command that requires sudo

But what if you need to run a command that requires sudo privileges on a remote server? If you do that, you'll see a tty error (Figure A).


How do you get around that? Fortunately, there's a little switch you can add to the command. Said switch is -t. What does -t do? It forces pseudo-terminal allocation, so ssh has no idea it doesn't have a local terminal to use.

So, to run a remote command, via ssh, that requires sudo privileges, the ssh command looks like:
ssh -t USER@SERVER_IP "sudo COMMAND"

Say, for instance, you want the user jack to upgrade a remote server at 192.168.1.201. This command is:
ssh -t jack@192.168.1.201 "sudo apt-get upgrade -y"


You will first be asked for the user's password for the SSH connection, followed by a second request for the user's password for sudo privileges (Figure B).

Figure B: A second request for the user's password.

The command will run as though it was executed on the local machine (only it's running on the remote machine). When the command completes, you'll return to the local prompt, ready to keep working.

And that's all there is to running commands that require sudo privileges on a remote machine, via SSH.