Set SSH connection timeout

Question

I m trying to cut down the time ssh is trying to open a connection to a host  If I put for example ssh www google com it takes very long until the prompt comes back   I read about using ssh -o ConnectTimeout 10 www google com instead  but even this takes very long  Is there maybe a number of attemps I can modify to decrease the blocking time

User · Answer

The ConnectTimeout option allows you to tell your ssh client how long you're willing to wait for a connection before returning an error. By setting ConnectTimeout to 1, you're effectively saying "try for at most 1 second and then fail if you haven't connected yet".

The problem is that when you connect by name, the DNS lookup can take several seconds. Connecting by IP address is much faster, and may actually work in one second or less. What sinelaw is experiencing is that every attempt to connect by DNS name is failing to occur within one second. The default setting of ConnectTimeout defers to the linux kernel connect timeout, which is usually pretty long.

User · Answer

The problem may be that ssh is trying to connect to all the different IPs that www google com resolves to  For example on my machine     ssh -v -o ConnectTimeout 1 -o ConnectionAttempts 1 www google com OpenSSH 5 9p1  OpenSSL 0 9 8t 18 Jan 2012 debug1  Connecting to www google com  173 194 43 20  port 22  debug1  connect to address 173 194 43 20 port 22  Connection timed out debug1  Connecting to www google com  173 194 43 19  port 22  debug1  connect to address 173 194 43 19 port 22  Connection timed out debug1  Connecting to www google com  173 194 43 18  port 22  debug1  connect to address 173 194 43 18 port 22  Connection timed out debug1  Connecting to www google com  173 194 43 17  port 22  debug1  connect to address 173 194 43 17 port 22  Connection timed out debug1  Connecting to www google com  173 194 43 16  port 22  debug1  connect to address 173 194 43 16 port 22  Connection timed out ssh  connect to host www google com port 22  Connection timed out   If I run it with a specific IP  it returns much faster   EDIT  I ve timed it  with time  and the results are    www google com - 5 086 seconds 173 94 43 16   - 1 054 seconds

[ssh] Set SSH connection timeout

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