Linux – RHEL/CENTOS SSH freezing randomly

centoslinuxredhatssh

I noticed following behavior on two of my CENTOS7 machines .. (it also happened on a RHEL6 too).

Sometimes meanwhile i'm typing, my session freezes. What I've already figured out.

Router shows connections as still active but as idle
ping has recorded no errors while transmitting packets (server got pinged the whole login)
I can immediately login to a second session, check the log and see following:

systemd-logind: New session 1 of user root.
systemd: Started Session 1 of user root.
systemd: Starting Session 1 of user root.
systemd-logind: New session 2 of user root.
systemd: Started Session 2 of user root.
systemd: Starting Session 2 of user root.

So the session, seems to be opened anyway. As soon as I close the freezed window systemd-logind: Removed session 1. appears.

There is no error "Write failed: Broken pipe", which appears after a disconnect.

I connect via BASH from my ubuntu desktop. It never happended to another Server. Just them. SSH is configured with default settings.

The machine is setted up new, it is a cluster and it appers on both nodes. Well actually the cluster isn't configured, they are just two server, setted up completey the same.

EDIT: I also noticed, that the freezed session is shown as active on the router, but idle since freeze, even with the session window closed ..

Best Answer

The configuration for this is in the file ~/.ssh/config. To send the signal every four minutes to remotehost, put the following in your ~/.ssh/config.

Host remotehost
  HostName remotehost.com
  ServerAliveInterval 240

This is what I have in my ~/.ssh/config.

To enable it for all hosts use:

Host * ServerAliveInterval 240

Also make sure to run chmod 600 ~/.ssh/config, because the config file must not be world-readable.

Related Solutions

Ssh – How to automate SSH login with password

Don't use a password. Generate a passphrase-less SSH key and push it to your VM.

If you already have an SSH key, you can skip this step… Just hit Enter for the key and both passphrases:

$ ssh-keygen -t rsa -b 2048
Generating public/private rsa key pair.
Enter file in which to save the key (/home/username/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/username/.ssh/id_rsa.
Your public key has been saved in /home/username/.ssh/id_rsa.pub.

Copy your keys to the target server:

$ ssh-copy-id id@server
id@server's password:

Now try logging into the machine, with ssh 'id@server', and check-in:

.ssh/authorized_keys

Note: If you don't have .ssh dir and authorized_keys file, you need to create it first

to make sure we haven’t added extra keys that you weren’t expecting.

Finally, check to log in…

$ ssh id@server

id@server:~$

You may also want to look into using ssh-agent if you want to try keeping your keys protected with a passphrase.

SSH – Bad Owner or Permissions on ~/.ssh/config

I needed to have rw for user only permissions on config. This fixed it.

chmod 600 ~/.ssh/config

As others have noted below, it could be the file owner. (upvote them!)

chown $USER ~/.ssh/config

If your whole folder has invalid permissions here's a table of possible permissions:

Path	Permission
.ssh directory (code)	0700 (drwx------)
private keys (ex: `id_rsa`) (code)	0600 (-rw-------)
`config`	0600 (-rw-------)
public keys (*.pub ex: `id_rsa.pub`)	0644 (-rw-r--r--)
`authorized_keys` (code)	0644 (-rw-r--r--)
`known_hosts`	0644 (-rw-r--r--)

Sources:

openssh check-perm.c
openssh readconf.c
openssh ssh_user_config fix_authorized_keys_perms

Best Answer

Related Solutions

Ssh – How to automate SSH login with password

SSH – Bad Owner or Permissions on ~/.ssh/config

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