64 bit Vs 32 bit Application

[Michael Selvesteen_2]

Folks,

I have deployed OpenSSH 4.0 which is a 32 bit application on a production server (11i Box).
Our requirement is that it should serve more than 600 concurrent ssh connections, but sshd fails to do so when it receives more connections. Will 64 bit SSHD help in this situation.

What are the advantages and disadvantages of 64 bit over 32 bit applications?

Please share your thoughts.

[Derek Whigham_1]

I would think that a 64Bit version would not help this situation. It's more likely that the system is running out of resources with so many users logged on, Check /var/adm/syslog/syslog.log for details of why the ssh logging is failing. And Post the output

[morganelan]

the advantages of 64 bit over 32 bit :
-higher performance
-increased system capacity parameters
-reduced swapping
64-bit integers, for
instance, provide the ability to operate on larger numbers in a single operation, improving performance for operations such as encryption, data copy, graphics, and large multimedia processes.

[Pedro Cirne]

Hi,

Post the output of:

#dmesg

and do

# sar -v 5 10

when the system stops accepting connections and post the ouput.

Enjoy :)

Pedro

[RAC_1]

What is the error that you get?? what kind of problems you experience when ssh users go above say 500??

[Paul Clayton]

Have you check for your PSeudo devices, and whther you have enough configured in the kernel.

[Ermin Borovac]

ssh is using streams based ptys so relevant kernel parameter to check is nstrpty.

Also you could play with sshd_config parameter MaxStartups. The following text comes from sshd_config man page.

MaxStartups
Specifies the maximum number of concurrent unauthenticated con-
nections to the sshd daemon. Additional connections will be
dropped until authentication succeeds or the LoginGraceTime
expires for a connection. The default is 10.

Alternatively, random early drop can be enabled by specifying the
three colon separated values â start:rate:fullâ (e.g.,
"10:30:60"). sshd will refuse connection attempts with a proba-
bility of â rate/100â (30%) if there are currently â startâ (10)
unauthenticated connections. The probability increases linearly
and all connection attempts are refused if the number of unau-
thenticated connections reaches â fullâ (60).

[Bill Hassell · Accepted solution]

ssh does not need 64bit features at all. Changing a process to 64bits will not improve performance UNLESS the process is already using 64bit computations. 64bits only helps with massive (gigabyte) sized programs. ssh only uses a few megs. As mentioned, sshd is not issuing a message about too many connectins, it has run out of device files for the connections. Run SAM and increase the following 3 parameters to 700:

npty 700
nstrpty 700
nstrtel 700

SAM will automatically extend the (very low) default of 60 connections by adjusting both the kernel parameters and also creating the additional device files. If you think you'll need more, bump it up to more than you'll need (1000? 5000?)

[Michael Selvesteen_2]

Hello All,

Thanks to everyone for the reply. I have tuned the kernel parameters and the problem goes away. Now my sshd handles more concurrent connection than before.

Thanks everyone for the timely help.