Protocols are a set of rules or standards that define the communication between devices on a network.
Generalities of a Service
A process is a running program at a particular instant of time.
The process refers to an opening of a Web Browser or any other visible program or action for the user, but this term also includes programs that are running in the background waiting to be called by the system. Those programs can be services that offer remote connection, sending of mail, or translation of IPs into readable URLs.
These services are identified by a number of ports defined by the Assigned Numbers RFC.
The configuration of services is in
/etc/services and includes the name, the port that defines the service, and which transport protocol is used (UDP or TCP) for each one.
This protocol enables secure connection to the SSH server on a remote machine.
Installation of the package
By default, in CentOS 7, the SSH package comes installed, but if not, please run:
yum install openssh openssh-server openssh-clients openssl-libs
It installs the openssh package to enable SSH as a server and as a client.
If you need additional information about yum commands, you can visit this link.
The default configuration file
The default configuration file and settings for the SSHD daemon is in
cp /etc/ssh/sshd_config /etc/ssh/sshd_config.ori
This creates a copy of the original configuration file in order to prevent damage or mistakes during a custom configuration.
Then, you can customize the configuration in the
/etc/ssh/ssh_configfile with these options:
Port 22 PermitRootLogin without-password PermitRootLogin yes PasswordAuthentication yes ForwardAgent yes ForwardX11 yes
Furthermore, to have the ability to run the protocol with the name of the servers such as
ssh server_name, create a file
~/.ssh/config, and customize it with:
Host shortcut_name HostName 0.1.2.3 Port 22 User x0y ServerAliveInterval 120 IdentityFile ~/.ssh/my_key.pem
Then, you will be able to enter the server called
shortcut_namewith SSH by using:
Restart the SSHD service
Once you make the configuration changes, you can save and close the file. For the changes to take effect, you should restart the SSH daemon.
systemctl restart sshd.service
This command is used in case the SSHD service is
enabled. To check the current status of the service, please read more about the status of a service.
Generate an SSH Key
To secure the transmission of information, SSH employs different types of data manipulation techniques that include forms of asymmetrical encryption such as an SSH key.
Enterto accept the default location and filename which is
~/.ssh/id_rsa. Then press
Enteragain to not set a passphrase when prompted.
Make sure the SSH key was successfully created by checking the encrypted content at
This file must have the permission 600. To check it please run
ls -AhlF ~/.ssh.
Finally, to copy the SSH key to a server, please run
ssh-copy-id -i ~/.ssh/id_rsa.pub user@server
This protocol allows files to be copied to, from, or between different hosts. It uses SSH for data transfer and provides the same authentication and same level of security as SSH.
Copy the file
remote_file.txtfrom a remote host to the local host
scp firstname.lastname@example.org:remote_file.txt /some/local/directory
Copy the file
local_file.txtfrom the local host to a remote host directory
scp local_file.txt email@example.com:/some/remote/directory
Copy the directory
local_directoryfrom the local host to a remote host's directory
scp -r local_directory firstname.lastname@example.org:/some/remote/directory/remote_directory
Copy the file
fr1.txtfrom remote host
rh1.ornl.govto remote host
scp email@example.com:/some/remote/directory/fr1.txt firstname.lastname@example.org:/some/remote/directory/
Copy multiple files from a local directory to a remote host home directory
scp one_file.txt another_file.txt email@example.com:
To set up
NFS mounts, we will need at least two Linux/Unix machines. Here we will be using two servers.
- NFS Server: ornlserver.org with IP-192.168.0.100
- NFS Client: ornlclient.org with IP-192.168.0.101
Configure export directory
For sharing a directory with NFS, we need to make an entry in the
/etc/exportsconfiguration file. Let's create a new directory named
/partition of the server.
Then, we need to make an entry in
/etc/exportsand restart the services to make our directory shareable in the network.
mkdir /nfsshare vi /etc/exports /nfsshare 192.168.0.101(rw,sync,no_root_squash) service autofs restart
It displays a directory in the
/partition named "nfsshare" which is being shared with client IP "192.168.0.101" with read and write privileges. You can also use the hostname of a server.
Mount a shared directory on an NSF client
To mount a directory in our server to access it locally, we need to find out what shares are available on the remote server or NFS Server with
showmount -e 192.168.0.100 Export list for 192.168.0.100: /nfsshare 192.168.0.101
This command shows that a directory named
nfsshareis available at "192.168.0.100" to share with your server.
To mount a shared NFS directory permanently, we can use following
vi /etc/fstab 192.168.0.100:/nfsshare /mnt nfs defaults 0 0 service autofs restart
vi /etc/fstab, we are setting the
IP:name_directoryto be mounted, and it will be mounted on
/mnt. You can verify it with
mount | grep nfs.