sudo nano /etc/hosts

See details on http://www.rackspace.com/knowledge_center/article/how-do-i-modify-my-hosts-file

netstat -anp

See details on https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/3/html/Security_Guide/s1-server-ports.html

sudo iptables -t nat -L -n

See details on http://ipset.netfilter.org/iptables.man.html

sudo apt-get install openssh-server 
sudo service sshd start

sudo service sshd start

See details on https://lecturesnippets.com/lesson/setting-up-ssh-server-in-centos-7-minimal-install/

This is a bad practice. Do not enable root login in production environment.

• Open /etc/ssh/sshd_config and change:
  • PermitRootLogin yes
  • PasswordAuthentication yes
• sudo service sshd restart

See details on:

• https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/V2V_Guide/Preperation_Before_the_P2V_Migration-Enable_Root_Login_over_SSH.html

• Add nameserver in this file

sudo nano /etc/resolvconf/resolv.conf.d/head

• Add search in this file

sudo nano /etc/resolvconf/resolv.conf.d/tail

• Update

sudo resolvconf -u

See details on http://www.lampnode.com/linux/howto-setup-nameserver-on-ubuntu-1404-by-resolvconf/

• Make nameserver permanent

Add PEERDNS=no to /etc/sysconfig/network-scripts/ifcfg-***.

See details on https://www.centos.org/forums/viewtopic.php?t=62970

sudo mount -t cifs \
     -o username=${name},password=${pwd},uid=${uid},gid=${gid} \
     ${network path} ${local path}

See details on http://unix.stackexchange.com/questions/68079/mount-cifs-network-drive-write-permissions-and-chown

scp SourceFile user@host:directory/TargetFile
scp user@host:directory/SourceFile TargetFile

See details on http://webdev.gmu.edu/uploading-files-with-secure-copy-scp/.

Configure the Firewall Using the Command Line:

sudo lokkit --port=123:udp --update

Checking Network Access for Incoming NTP Using the Command Line

sudo less /etc/sysconfig/system-config-firewall

See details on https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Deployment_Guide/s2-Configure_the_Firewall_Using_the_CLI.html.

curl -v -X PUT -d <content> http://localhost/api/handler

curl http://localhost/somefile.zip > /tmp/myfile.zip

• Use ifconfig and know which NIC we are updating.
• Open /etc/sysconfig/network-scripts/ifcfg-??? and change:
  • BOOTPROTO=none
  • ONBOOT=yes
  • DNS1=???
  • DOMAIN=??
  • IPADDR=??
  • PREFIX=24
  • GATEWAY=??
• sudo systemctl restart network

Or, use UI tool:

sudo nmtui

See details on:

• https://www.cyberciti.biz/faq/howto-setting-rhel7-centos-7-static-ip-configuration/
• http://ask.xmodulo.com/configure-static-ip-address-centos7.html

After installing CentOS in Virtual Box, the VM is not ready to use NAT network connection. We need to enable DHCP and restart network.

• Edit this config file:

sudo nano /etc/sysconfig/network-scripts/ifcfg-enp3s0

• Add the following configurations:

DEVICE=enp3s0
ONBOOT=yes
DHCP=yes

• Restart network:

sudo ifdown enp0s3
sudo ifup enp0s3

See details on:

• https://www.serverlab.ca/tutorials/linux/administration-linux/how-to-configure-centos-7-network-settings/

sudo systemd-resolve --flush-caches
dig <FQDN>

See details on:

• https://askubuntu.com/questions/2219/how-do-i-clear-the-dns-cache

Intranet

nmblookup -A <IP address>

Internet

nslookup <IP address>