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== Want to install telnet? =={{:CentOS_Linux_Distribution_Enable_Telnet}} telnet server is not recommended for security reasons, plain text over tcp/ip # yum install telnet telnet-server -y How about telnet client? It is not installed by default. #yum intall telnet -y The package is Package telnet.i686SELinux users and roles are not related to the actual system users and roles.[[SELinux]] users and roles are not related to the actual system users and roles.== vi editor vim syntax highlighting ==On CentOS the command 'vi' and 'vim' by default, both open the vim editor (vim enhanced), however, with some differences. The vi command utilizes what is known as 'Small version without GUI' while executing the vim command utilizes 'Huge version without GUI', both when executed from the console respectively. You can test this by using the :version command within the vim editor. Another way to see the differences is to execute the following from the shell: vi --version | fgrep syntax vim --version | fgrep syntaxIf -syntax is on the line, you don't have syntax highlighting compiled in. If +syntax is on the line, then it does. Note that on CentOS you will see different options for vi as opposed to vim. Unlike some Fedora versions, and variants like Trustix, it is not an issue with only vim minimum installed, this is not the case. See by the version output on CentOS both are using vim enhanced.The vi command points to /bin/vi while the vim command points to /usr/bin/vim yet they both use vim enhanced. The fastest solution is to do the following: mv /bin/vi /bin/vi.small ln -s /usr/bin/vim /bin/viIf your system doesn't have the vim enhanced package installed, simply install with yum; 'yum install vim-enhanced'== Startup Troubleshooting ===== failed to start crash recovery kernel arming ===Problems after power loss or crash, the crash kernel error message. You can fix by making simple change to grub and reboot. vi /etc/default/grubchange "crash kernel=auto" to "crash kernel=512M" then type the following command grub2-mkconfig -o /boot/grub2/grub.cfg=== sshd or other service wont start because system clock is wrong ===Some useful commands to correct system clock so services run correctly. hwclock -r shows cmos time date +%Y%m%d -s "20170618" set the linux date date +%T -s "19:25:00" set the linux time hwclock -w force cmos clock to match linux clock hwclock -hctosys force linux clock to match cmos clock=== sshd or other service wont start because of selinux ===You can disable selinux and then try to start the service. This will allow you to test and determine if selinux isthe culprit so that you can make adjustments to selinux. setenforce 0 sestatusIf you need selinux to remain permissive after reboot for testing purposes, vi /etc/selinux/configChange #SELINUX=enforcing SELINUX=permissive=== system uses postfix to receive email ===You can manually start postfix systemctl start postfix systemctl status postfix=== system uses dovecot for secure socket pop and imap ===You can manually start dovecot systemctl start dovecot systemctl status dovecot[[Category:Linux Distributions]]