Posts filed under ‘Red Hat’

Oracle Direct I/O on Linux

Two documents about Direct I/O and Asynchronous I/O on Linux:
Tuning Oracle Database 10g for ext3 file systems
Tuning and Optimizing Red Hat Enterprise Linux for Oracle 9i and 10g Databases

October 7, 2009 at 12:38 pm Leave a comment

More on network card bonding

Two useful articles from RedHat KnowledgeBase:

How do I configure Multiple Bonds in Red Hat Enterprise Linux 5 with different bonding modes?

What network bonding modes are available in Red Hat Enterprise Linux 5?

May 11, 2009 at 1:30 pm Leave a comment

Checking time zone information on RHEL5

[user@server ~]$ /usr/sbin/zdump -v /usr/share/zoneinfo/Asia/Karachi |grep 2009
/usr/share/zoneinfo/Asia/Karachi Tue Apr 14 18:59:59 2009 UTC = Tue Apr 14 23:59:59 2009 PKT isdst=0 gmtoff=18000
/usr/share/zoneinfo/Asia/Karachi Tue Apr 14 19:00:00 2009 UTC = Wed Apr 15 01:00:00 2009 PKST isdst=1 gmtoff=21600
/usr/share/zoneinfo/Asia/Karachi Sat Oct 31 17:59:59 2009 UTC = Sat Oct 31 23:59:59 2009 PKST isdst=1 gmtoff=21600
/usr/share/zoneinfo/Asia/Karachi Sat Oct 31 18:00:00 2009 UTC = Sat Oct 31 23:00:00 2009 PKT isdst=0 gmtoff=18000

April 30, 2009 at 11:00 am Leave a comment

RHEL5 – remote graphical Linux

To allow remote graphical linux desktop access the following changes are required in /etc/gdm/custom.conf .

Add two enties to the existing categories:

[security]
DisallowTCP=false

[xdmcp]
Enable=true

March 30, 2009 at 11:08 am Leave a comment

Applying Security patches in RedHat

Since RHEL 5.1 Redhat introduced yum-security package which can be used to limit yum to retrieve only security-related updates. To install it execute:

yum install yum-security

Related Commands:

yum list-sec

yum update –security

More information in Red Hat Magazine: Tips and tricks: yum-security

October 23, 2008 at 2:55 pm Leave a comment

VNC Server on Red Hat Enterprise Server 4

To Enable VNC on Red Hat Enterprise Server 4;
a) make sure it is installed
rpm -qi vnc-server

b) Edit /etc/sysconfig/vncservers and add the following line:

VNCSERVERS="1:root"

c) Edit /root/.vnc/xstartup file and uncomment the following two lines
unset SESSION_MANAGER
exec /etc/X11/xinit/xinitrc

d) Specify password for vnc session
vncpasswd

e) start vncserver
/etc/init.d/vncserver start
To make sure it starts automatically at boot time:
chkconfig vncserver on

f) On your browser go to the following url:
http://yourlinuxserver:5801

g) It should start java vnc session and allow you to login.

May 7, 2008 at 10:10 am Leave a comment

Red Hat sysstat service

While tools like vmstat, top, free allow us to gain insight into system performance they offer little help if to monitor various system statistics over longer period of time.

This is why Red Hat includes systat service that allows administrators to monitor system performance.

Sysstat includes the following tools:

– mptstat – to monitor CPU
– iostat – to monitor disk usage
– sadc – system activity data collector.
– sar – collect, report, or save system activity information.

How long logs should be kept on the system (default is 7 days). This is adjustable parameter and can be changed in /etc/sysconfig/sysstat file

How often data is collected?

By default the statistics are collected every 10 minutes but it can be customized in /etc/cron.d/sysstat file. Additionally daily summary of process accounting is generated.

Content of /etc/cron.d/sysstat file:

# run system activity accounting tool every 10 minutes
*/10 * * * * root /usr/lib/sa/sa1 1 1
# generate a daily summary of process accounting at 23:53
53 23 * * * root /usr/lib/sa/sa2 -A

You could change the first line to the as follows to probe system every minute:

*/1 * * * * root /usr/lib/sa/sa1 1 1

Once a minute is probably a little bit excessive. I would suggest leaving default setting (every 10 min) and only change it to probe more often if specific issue has to be troubleshooted on a server.

How to read the data?

To retrieve statistics:
sar -u – CPU utilization
sar -b – report I/O and transfer rate statistics
sar -w – swap usage
sar -q – system load
sar -R – memory statistics
sar -B – kernel paging performance
sar -n ALL – report network statistics
sar -n EDEV – report network errors
sar -v – report status of inode, file and other kernel tables

Where are the disk usage statistics?

Default configuration does not probe for disk usage statistics. Monitoring disk I/O usage will increase significantly amount of data stored in logfiles generated by sysstat. To enable it edit the lines in /usr/lib/sa/sa1:
Before:

exec ${ENDIR}/sadc -F -L 1 1 –
exec ${ENDIR}/sadc -F -L $* –

After:

exec ${ENDIR}/sadc -F -d -L 1 1 –
exec ${ENDIR}/sadc -F -d -L $* –

Once disk usage monitoring is enabled. Statistics can be displayed with the following command:

sar -d -p

What about reading older data?

For older reports we can extract data from filename:

ex.
sar -p -f /var/log/sa/sa14
(where sa14 file contains statistics for 14th day of the month ex. Apr 14)

April 17, 2008 at 10:11 am Leave a comment

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