02-29-2012 10:45 AM
security is sftping about 50 files to my hpux server, about 5 didnt come over. its intermittent. and
he says they send the files in parallel not serieally.
the admin is asking me:
what is the maximum concurrent connections for sftp/ssh for hpux?
has anyone come seen this?
thx in advance
03-01-2012 07:18 AM
SSH needs a lot of high-quality random numbers for generating session keys. Computers are normally very deterministic, and so generating truly random numbers is a very difficult task for a computer.
If your HP-UX is 11.11 or older, it may not have a kernel-based random number generator accessible via /dev/random and /dev/urandom. For 11.11, the KRNG was/is available as free optional software from software.hp.com; older versions don't have it at all.
If /dev/random and /dev/urandom do not exist or your SSH package is too old to use them, SSH generates random numbers for session keys by running some commands listed in /opt/ssh/etc/ssh_prng_cmds and hashing the output. This is a very portable but very inefficient method: even a powerful system can run out of random numbers if this method is used and the system needs to quickly establish many connections in parallel.
Otherwise, the number of concurrent connections is limited only by the number of available network sockets, system performance and available memory.
My recommendations would be:
- make sure your HP SSH is reasonably up-to-date
- if you have HP-UX 11.11, download the KRNG11i package from software.hp.com and install it (it's a kernel driver, so it'll require a reboot to install)
04-12-2012 12:44 AM
There are no restrictions on the number of concurrent authenticated SSH/sftp connections that can be established. It is dependent of the system's CPU, memory and sockets available for allocation.
However you can control the number of concurrent unauthenticated SSH connections using the sshd_config directive MaxStartups.
Ssh connections are also limited by the number of pseudo-ttys. You can use -t or -T option to establish a session without pseudo-tty.
04-13-2012 06:19 PM
Its 2 seconds
Proverbs 3:5,6 Trust in the Lord with all your heart and lean not on your own understanding; in all your ways acknowledge him, and he will make all your paths straight.