I have a script that sends 8 files to the same server. Running all 8 commands separately works, but when I run the script, the 5th scp command will timeout after the 4 previous files are transferred.

I replaced the 5th command with a simple ssh command with -vvv turned on and get the following messages:

OpenSSH_5.3p1, OpenSSL 1.0.1e-fips 11 Feb 2013
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to [] port 22.
debug1: connect to address port 22: Connection timed out
ssh: connect to host port 22: Connection timed out

I've also tried tuning the following values in /etc/ssh/sshd_config on the server I'm sending files to. ClientAliveCountMax, MaxSessions, MaxAuthTries, but none of them solved the problem. (note: have restarted sshd after editing file)

Any thoughts on what else might be the problem?


A likely explanation is that the server has a firewall which is throttling SSH connections (not uncommon to avoid bots incessantly trying to find a password). If it's UFW, use:

ufw status

to list the current values. You should see (among other things):

To Action  From
22 LIMIT   Anywhere                  

You can lift the restriction for specific addresses using

ufw insert 1 allow in from nnn.nnn.nnn.nnn

If it's raw iptables, then it's the same idea but the adequate commands are beyond my expertise (be careful to not fence you off your server).

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