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I am running OpenSSH_6.5 with UsePAM yes in my board.

I have observed that with UsePAM no in /etc/ssh/sshd_config, sshd runs slower than previous case.

How is this possible? My understanding is that without pam, sshd must execute faster than with pam.

Here is sshd_config

$ cat /etc/ssh/sshd_config 
#       $OpenBSD: sshd_config,v 1.82 2010/09/06 17:10:19 naddy Exp $

# This is the sshd server system-wide configuration file.  See
# sshd_config(5) for more information.

# This sshd was compiled with PATH=/usr/bin:/bin:/usr/sbin:/sbin

# The strategy used for options in the default sshd_config shipped with
# OpenSSH is to specify options with their default value where
# possible, but leave them commented.  Uncommented options change a
# default value.

#Port 22
#AddressFamily any
#ListenAddress 0.0.0.0
#ListenAddress ::

# The default requires explicit activation of protocol 1
#Protocol 2

# HostKey for protocol version 1
#HostKey /etc/ssh/ssh_host_key
# HostKeys for protocol version 2
#HostKey /etc/ssh/ssh_host_rsa_key
#HostKey /etc/ssh/ssh_host_dsa_key
#HostKey /etc/ssh/ssh_host_ecdsa_key

# Lifetime and size of ephemeral version 1 server key
#KeyRegenerationInterval 1h
#ServerKeyBits 1024

# Logging
# obsoletes QuietMode and FascistLogging
#SyslogFacility AUTH
#LogLevel INFO

# Authentication:

#LoginGraceTime 2m
#PermitRootLogin yes
#StrictModes yes
#MaxAuthTries 6
#MaxSessions 10

#RSAAuthentication yes
PubkeyAuthentication no
#AuthorizedKeysFile     .ssh/authorized_keys

# For this to work you will also need host keys in /etc/ssh/ssh_known_hosts
#RhostsRSAAuthentication no
# similar for protocol version 2
#HostbasedAuthentication no
# Change to yes if you don't trust ~/.ssh/known_hosts for
# RhostsRSAAuthentication and HostbasedAuthentication
#IgnoreUserKnownHosts no
# Don't read the user's ~/.rhosts and ~/.shosts files
#IgnoreRhosts yes

# To disable tunneled clear text passwords, change to no here!
#PasswordAuthentication yes
#PermitEmptyPasswords no

# Change to no to disable s/key passwords
#ChallengeResponseAuthentication yes

# Kerberos options
#KerberosAuthentication no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes
#KerberosGetAFSToken no

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

# Set this to 'yes' to enable PAM authentication, account processing, 
# and session processing. If this is enabled, PAM authentication will 
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication.  Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
UsePAM yes

#AllowAgentForwarding yes
AllowTcpForwarding no
#GatewayPorts no
X11Forwarding no
#X11DisplayOffset 10
#X11UseLocalhost yes
#PrintMotd yes
PrintLastLog no
#TCPKeepAlive yes
#UseLogin no
UsePrivilegeSeparation no
#PermitUserEnvironment no
#Compression delayed
#ClientAliveInterval 0
#ClientAliveCountMax 3
UseDNS no
#PidFile /var/run/sshd.pid
#MaxStartups 10
#PermitTunnel no
#ChrootDirectory none

# no default banner path
#Banner none

# override default of no subsystems
Subsystem       sftp    /libexec/sftp-server

# Example of overriding settings on a per-user basis
#Match User anoncvs
#       ForceCommand cvs server
Port 22
ClientAliveInterval 0
ClientAliveCountMax 0

And /etc/pam.d/sshd

$ cat /etc/pam.d/sshd 
#%PAM-1.0
auth    sufficient      pam_ldap.so
auth    sufficient      pam_unix.so use_first_pass
account sufficient      pam_ldap.so
account sufficient      pam_unix.so
session required        pam_ldap.so
session required        pam_unix.so
share|improve this question
    
What is 'faster'? The login process using ssh, file transfer using scp, or something else? Do you have some measured values? –  Anthon Apr 1 at 5:08
    
login process using ssh is faster with pam,without pam login process is slower –  user3184706 Apr 1 at 5:27
    
PAM doesn't intrinsically make authentication slower (not by a measurable amount). It depends what authentication methods you use. How did you configure things? Tell us how you compiled sshd, post the sshd_config file, and post the PAM configuration. –  Gilles Apr 1 at 22:12
    
@Gilles:Posted sshd_config and /etc/pam.d/sshd –  user3184706 Apr 2 at 4:22

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