Friday, 2 December 2011

Useful links etc

TBC - just a bunch of useful links

Port Forwarding

ssh -L localport:localhost:remoteport remotehost

Hadoop rebuild

rm -rf /data/hdfs
rm -rf /data/tmpd_hdfs
hadoop namenode -format

Emailing attachment on Linux (CentOS 6.1)

mailx -s "Example send PDF file" -a mypdf.pdf <
pdf test mail

Other info


Check for FC

# fcinfo hba-port
No Adapters Found

# fcinfo hba-port|grep -i wwn
HBA Port WWN: 2100001b321c25ba
        Node WWN: 2000001b321c25ba
HBA Port WWN: 2101001b323c25ba
        Node WWN: 2001001b323c25ba
HBA Port WWN: 2100001b321c08b9
        Node WWN: 2000001b321c08b9
HBA Port WWN: 2101001b323c08b9
        Node WWN: 2001001b323c08b9

pgp (Network Associates Freeware version)

To view keys on keyring
/opt/PGP/pgp -kv

To add key to keyring
/opt/PGP/pgp -ka

To edit the trust level of the 's key
/opt/PGP/pgp -ke [keyring]

To pgp encrypt a bunch of files (in this example a directory full of *.gz files
userid=xxxxxx    # the userid associated with the recipient's public key
for f in `ls *.gz`
  echo $f
  if [ ! -f ${f}.pgp ]
    /opt/PGP/pgp -e $f $userid
    if [ $? -ne 0 ]
      echo "ERROR: Unable to pgp encrypt file: $f"
      exit 1

Stop/start Solaris service - e.g. httpd

svcadm -v enable /network/http:apache2
svcadm -v disable /network/http:apache2

Swappiness in Linux

See Scott Alan Miller's (SAM's) article on swappiness
He says ...
"On a latency sensitive system or a system where disk IO is at a premium, lowering this number is generally advisable".
So for hadoop which is typically disk IO centric, you want to lower this - even set it to 0.
On Linux system run:
sysctl vm.swappiness
grep vm.swappiness /etc/sysctl.conf 
To set to 0:
sysctl vm.swappiness=0

echo "vm.swappiness = 0" >> /etc/sysctl.conf

For virtualised system he recommends setting to 10.
And to profile performance before and after the change.

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