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What software can I use to provide the same features as SSH (openssh-server)? I have a busy server that I am losing all SSH connectivity once in a while. I can't find a solution to yet, we are investigating the possible causes but meanwhile we want to have a safe alternative, so we weren't locked out again (and have to reboot the server).

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up vote 2 down vote accepted

You can try other SSH servers such as lsh or Dropbear, which have less features and are not as thoroughly tested, but can be a good temporary alternative regardless.

There exists a Telnet server netkit-telnet-ssl which supports SSL/TLS encryption and authentication. However, even though TLS can provides sufficient security (provided the sysadmin is not lazy and obtains a SSL certificate), Telnet remains a generally poorly designed protocol for daily use.

The Telnet and rlogin servers from Heimdal and MIT krb5-appl Kerberos suites have support for Kerberos authentication and encryption; however, the crypto code in MIT telnetd is limited to DES64, and rlogin is from my experience even more of a pain in the ass to set up than Telnet.

Finally, check the system log, optionally after increasing LogLevel in sshd_config. You might just find the cause of SSH loss.

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Can I also install openssh from source and run on another port? Or it will conflict with the other, too? – Jhonny Everson Jan 4 '12 at 16:06
@JhonnyEverson: It might conflict, but if it uses autoconf then ./configure --prefix=/opt/openssh should work. – grawity Jan 4 '12 at 16:08
thank you. I'll try that. – Jhonny Everson Jan 4 '12 at 16:10

Since the sshd of Openssh has a -f config_file and a -p port option I surmise that you can run two of them concurrently on different ports (using distinct config files if necessary) - one could be used only in the event of problems with the first and could be more tightly restricted.

You'd have to set up the startup scripts appropriately (rc.local?) or run one out of (x)inetd?

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