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Top Forums UNIX for Advanced & Expert Users OEL 6.3 :Slow login due to /etc/ssh/sshd_config configuration Post 302810201 by John K on Tuesday 21st of May 2013 11:29:28 AM
Old 05-21-2013
OEL 6.3 :Slow login due to /etc/ssh/sshd_config configuration

Version: Oracle Enterprise Linux 6.3
Running on VMWare Workstation


When I login to my Linux VM from putty, the third line prompting for password comes only after few seconds.

Code:
login as: root
Access denied
root@192.168.0.235's password: ---> It takes around 5 seconds to get this prompt

I managed to fix this issue after several trial and error experiments.
I have to do both Step1 and Step2 mentioned below to fix this issue. Doing either one of Step1 and Step2 won't fix the issue

Step1.
In
Code:
/etc/ssh/sshd_config file

Comment the line
Code:
GSSAPIAuthentication yes

and
Remove the comment for the line
Code:
 GSSAPIAuthentication no

sshd_config file should look like below

Code:
grep GSSAPI /etc/ssh/sshd_config
# GSSAPI options
GSSAPIAuthentication no
#GSSAPIAuthentication yes
#GSSAPICleanupCredentials yes
GSSAPICleanupCredentials yes
#GSSAPIStrictAcceptorCheck yes
#GSSAPIKeyExchange no

Step2. In /etc/ssh/sshd_config file
I commented the line
Code:
UseDNS yes

and then
uncommented
Code:
UseDNS no


and did a restart using
Code:
/etc/init.d/sshd restart

Soon, I'll have to use DNS functionality for this VM. So, I am worried that the above change ("UseDNS no") will prevent the VM from using the DNS service.
Is there any other workaround to make the login quick?
 

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LOGIN(8)						      System Manager's Manual							  LOGIN(8)

NAME
login.krb5 - kerberos enhanced login program SYNOPSIS
login.krb5 [-p] [-fFe username] [-r | -k | -K | -h hostname] DESCRIPTION
login.krb5 is a modification of the BSD login program which is used for two functions. It is the sub-process used by krlogind and telnetd to initiate a user session and it is a replacement for the command-line login program which, when invoked with a password, acquires Ker- beros tickets for the user. login.krb5 will prompt for a username, or take one on the command line, as login.krb5 username and will then prompt for a password. This password will be used to acquire Kerberos Version 5 tickets (if possible.) It will also attempt to run aklog to get AFS tokens for the user. The version 5 tickets will be tested against a local krb5.keytab if it is available, in order to verify the tickets, before letting the user in. However, if the password matches the entry in /etc/passwd the user will be unconditionally allowed (permitting use of the machine in case of network failure.) OPTIONS
-p preserve the current environment -r hostname pass hostname to rlogind. Must be the last argument. -h hostname pass hostname to telnetd, etc. Must be the last argument. -f name Perform pre-authenticated login, e.g., datakit, xterm, etc.; allows preauthenticated login as root. -F name Perform pre-authenticated login, e.g., datakit, xterm, etc.; allows preauthenticated login as root. -e name Perform pre-authenticated, encrypted login. Must do term negotiation. CONFIGURATION
login.krb5 is also configured via krb5.conf using the login stanza. A collection of options dealing with initial authentication are pro- vided: krb5_get_tickets Use password to get V5 tickets. Default value true. krb_run_aklog Attempt to run aklog. Default value false. aklog_path Where to find it [not yet implemented.] Default value $(prefix)/bin/aklog. accept_passwd Don't accept plaintext passwords [not yet implemented]. Default value false. DIAGNOSTICS
All diagnostic messages are returned on the connection or tty associated with stderr. SEE ALSO
rlogind(8), rlogin(1), telnetd(8) LOGIN(8)
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