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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.i686== 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]]