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While in many cases the ssh_exchange_identification: connection is closed due to an error on the remote host, problems with the hosts.deny and hosts.allow configuration files can cause problems, but there are other things that can cause the problem. If you are reading this, then you have probably already checked that these two files do not prevent your IP address from using ssh on a remote server.
Assuming this is the case, it could be a dependency problem, related to memory fragmentation or even excessive sessions from individual clients. The good news is that once the problem is solved, you should no longer see the error.
Check for Missing Dependencies
- This error usually occurs after a Glibc or OpenSSL update, and the server could not be restarted.
- While many distributions can install the update to glibc or OpenSSL and do not require a reboot, yours may not fall into the same category.
- If you know that the update is installed for Glibc, use lsof to see where the SSHD has open files.
- If you are using Ubuntu or Debian, use the upgrade command to get and install new packages. This will help you solve problems that may have occurred due to broken packages.
Fixing Memory Fragmentation
If that doesn’t help, you may have a problem on the host side of the equation. Hosts running in a VM don’t always have a swap partition, which can lead to memory fragmentation. Access the host by other means, perhaps physically, and then restart services that are experiencing problems. MySQL, Apache, nginx and other such services may be the culprits.
Although it may not always be possible to restart the host, this may solve the problem and may be a good idea if you have been going back and forth between this error message and the one returning an IP address. Remember that if you have any access to the server, you can run the vmstat -s command and get important statistics on how memory is used in many cases like a normal user.
Check out the Additional SSH Sessions
- Users may have exceeded the maximum number of SSH sessions without knowing it.
- Try cleaning up old sessions, then reconnect to the server.
- You should see only one or two users logged on at any one time. To check whether more than one SSH instance is running, use the who command.
- If more than two users are logged on, terminate user processes one after the other.
- Reconnect to the server using SSH and check for enhancements.
- This problem occurs when SSH cannot follow a script that launches several consecutive SSH sessions. You can also delay the SSH session with the sleep command.
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CCNA, Web Developer, PC Troubleshooter
I am a computer enthusiast and a practicing IT Professional. I have years of experience behind me in computer programming, hardware troubleshooting and repair. I specialise in Web Development and Database Design. I also have a CCNA certification for Network Design and Troubleshooting.