RHCE Series: SSH and NTP
Configure key-based authentication.
Configure additional options described in documentation.
Synchronize time using other NTP peers.
In Red Hat 6 (and I'm sure in 5 as well), public key authentication is enabled by default, but if you're unsure, you can uncomment the option and verify that it is set to yes.
[[email protected] ~]# vim /etc/ssh/sshd_config
[[email protected] ~]# egrep 'PubkeyAuthentication|AuthorizedKeysFile' /etc/ssh/sshd_config
[[email protected] ~]# service sshd restart
Stopping sshd: [ OK ]
Starting sshd: [ OK ]
Once that is complete. We can go to our client pc, generate keys, and copy the public key over.
[[email protected] ~]# ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
c6:83:f5:86:ad:cf:06:d3:73:f6:22:8f:0a:a7:06:99 [email protected]
The key's randomart image is:
+--[ RSA 2048]----+
| . |
| + + |
| o. S.+ |
| E .o+o o |
| .. oo + . |
| .+ oo.. . |
| .. .o+o.. |
[[email protected] ~]# ssh-copy-id -i ~/.ssh/id_rsa.pub 192.168.1.1
The authenticity of host '192.168.1.1 (192.168.1.1)' can't be established.
RSA key fingerprint is 40:f4:04:4b:68:53:92:55:82:f2:f4:68:db:0a:14:4f.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.1.1' (RSA) to the list of known hosts.
[email protected]'s password:
Now try logging into the machine, with "ssh '192.168.1.1'", and check in:
to make sure we haven't added extra keys that you weren't expecting.
Once that has completed, we can ssh to 192.168.1.1 (server1) from client1 without a password, but use a private / public key exchange.
Now, let's configure ntp.
[[email protected] ~]# date
Sun Oct 28 04:32:13 CDT 2012
[[email protected] ~]# yum -y install ntp
[[email protected] ~]# grep server /etc/ntp.conf
# Use public servers from the pool.ntp.org project.
#broadcast 192.168.1.255 autokey # broadcast server
#broadcast 126.96.36.199 autokey # multicast server
#manycastserver 188.8.131.52 # manycast server
#server 127.127.1.0 # local clock
[[email protected] ~]# ntpdate 0.centos.pool.ntp.org
27 Oct 23:33:34 ntpdate: step time server 184.108.40.206 offset -17998.779036 sec
[[email protected] ~]# date
Sat Oct 27 23:33:37 CDT 2012
[[email protected] ~]# service ntpd start
Starting ntpd: [ OK ]
[[email protected] ~]# ntpq -p
remote refid st t when poll reach delay offset jitter
mirror 220.127.116.11 2 u 8 64 1 48.895 1.225 0.000
18.104.22.168 22.214.171.124 2 u 7 64 1 54.330 0.806 0.000
ntp1.Housing.Be 126.96.36.199 2 u 6 64 1 51.920 -6.134 0.000
If you want to use other peers, you can modify the 'server' directive in /etc/ntpd.conf. Besure to use 'chkconfig' to make ntpd persistent.