asr.tech.notes

Here is the quick how-to for enabling and disabling SELinux on a Red Hat Enterprise Linux server temporarily and permanently.  There are 3 modes available with the SELinux- Enforcing – SELinux policy is enforced and access is denied based on the SELinux policy rules. Permissive – SELinux policy is not enforced .  Access is is not denied, but what would have been denied if it were enforced will be logged. Disabled – SELinux is disabled completely.  only DAC rules are used.  To permanently disable SELinux on the system, update ‘ SELINUX=disabled ’ in /etc/selinux/config file and reboot the system for the change to take effect To change between the modes temporarily during run time, use the /usr/sbin/setenforce command with the appropriate mode /usr/sbin/setenforce 1 will set the mode to Enforced /usr/sbin/setenforce 0 will set the mode to Permissive /usr/sbin/getenforce to display the current mode Refer RHEL 6 SELinux guide for more detailed informa...

Some useful links for analyzing Crash Dumps: Quick overview of Kernel Crash Dump Analysis http://magazine.redhat.com/2007/08/15/a-quick-overview-of-linux-kernel-crash-dump-analysis/ Crash Facility – White paper http://people.redhat.com/anderson/crash_whitepaper/ More about Oops messages: http://lxr.linux.no/linux/Documentation/oops-tracing.txt

Here is the list of steps to reduce the  root file system (lv_root) on a RHEL 6 Linux server: Boot the system into rescue mode. Do not mount the file systems (select the option to 'Skip' in the rescue mode and start a shell) Bring the Volume Group online #lvm vgchange -a -y Run fsck on the FS #e2fsck -f /dev/vg_myhost/lv_root Resize the file system with new size #resize2fs -f /dev/vg_myhost/lv_root 20G Reduce the Logical Volume of the FS with the new size #lvreduce -L20G /dev/vg_myhost/lv_root Run fsck to make sure the FS is still ok #e2fsck -f /dev/vg_myhost/lv_root Optionally mount the file system in the rescue mode #mkdir -p /mnt/sysimage/root #mount -t ext4 /dev/mapper/vg_myhost-lv_root /mnt/sysimage/root #cd /mnt/sysimage/root Unmount the FS #cd #umount /mnt/sysimage/root Exit rescue mode and boot the system from the hard disk #exit Select the reboot option from the recue mode

http://www14.software.ibm.com/webapp/set2/sas/f/vios/documentation/perf.html Reproduced from the link posted above: The VIOS online pubs in InfoCenter include sections on sizing for both Virtual SCSI and SEA. http://publib.boulder.ibm.com/infocenter/eserver/v1r2s/en_US/index.htm For Virtual SCSI, please see the section titled "Virtual SCSI Sizing Considerations". For SEA, please see the section titled "Planning for shared Ethernet adapters." QOS considerations The Virtual I/O server is a shared resource that can be shared concurrently by Virtual SCSI and by Virtual Ethernet / Shared Ethernet. Depending on the specific configuration of a Virtual I/O server, quality of service issues (long response times) may be encountered if insufficient CPU resources exist on the I/O server partition for the I/O load required. Recommendations for sizing and tuning the Virtual I/O server are discussed in the following paragraphs. The Virtual Ethernet and Shared Ethernet drivers ...

First, list all the HBAs, in the output below the HBA device name is /dev/td0 and /dev/td1 my-hp-system# ioscan -fnkC fc Class I H/W Path Driver S/W State H/W Type Description ================================================================= fc 0 0/4/0/0 td CLAIMED INTERFACE HP Tachyon TL/TS Fibre Channel Mass Storage Adapter /dev/td0 fc 1 0/7/0/0 td CLAIMED INTERFACE HP Tachyon TL/TS Fibre Channel Mass Storage Adapter /dev/td1 Now, use the fcmsutil to find the WWN and other information related to each of these HBAs: my-hp-system# fcmsutil /dev/td0

Here is a easy way to find the top paging space users using a svmon command: my-system> svmon -P -O sortseg=pgsp Unit: page -------------------------------------------------------------------------------      Pid Command          Inuse      Pin     Pgsp  Virtual 2289864 sshd             18908     7988        0    18414 2265260 ksh              18499     7988        0    18427 1765570 svmon            17398     8032        0    17337

The easiest way to test throughput between 2 AIX servers is to do a FTP test, generating data transfer with ‘dd’ command.  This will provide the throughput/speed for the specified amount of data transfer: #src-system> ftp dst-system … … ftp>  put "|dd if=/dev/zero bs=32k count=10000" /dev/null 200 PORT command successful. 150 Opening data connection for /dev/null. 10000+0 records in 10000+0 records out 226 Transfer complete. 327680000 bytes sent in 1.406 seconds (2.277e+05 Kbytes/s) local: |dd if=/dev/zero bs=32k count=10000 remote: /dev/null ftp>bye   This is the same test IBM recommends in the redbook and also during a support call