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Showing posts from November, 2008

sdparm: a utility for SCSI device

You may have heard of hdparm - a utility for getting info and changing certain parameters for IDE-type hard disk. It can't be used for SCSI hard disk though. So is there any similar utility for scsi hard disk? Yes there's one utility called with almost the same name: sdparm.

You may think that it has the same or at least similar to hdparm. No it is not. Well let's see what we can do with it below.

How to install it?
Ubuntu/Debian: apt-get install sdparm
Mandriva: urpmi sdparm
Redhat: yum install sdparm

A few examples:
list common mode parameters of a disk
sdparm /dev/sda

Sample output:
/dev/sda: COMPAQ BF03697B5A HPB2
Read write error recovery mode page:
AWRE 1 [cha: y, def: 1, sav: 1]
ARRE 1 [cha: y, def: 1, sav: 1]
PER 1 [cha: y, def: 1, sav: 1]
Caching (SBC) mode page:
WCE 0 [cha: y, def: 1, sav: 0]
RCD 0 [cha: y, def: 0, sav: 0]
Control mode page:
SWP 0 [cha: y, def: 0, sav: 0]
Informational except…

NAT and ip forwarding

NAT (be it SNAT or DNAT) relies on ip forwarding. You enable it, they are effective. I forgot to think about it last time ( I think 3 months ago) I setup Linux as a router. This is because server distros, enable it by default. Some distros however do not and most of them distros targeted for desktop/home users (pls check all popular distros to confirm). To enable it, you have to run this 2 commands:

sysctl -w net.ipv4.ip_forward=1
sysctl -p /etc/sysctl.conf
Of course you have to root to run those.

The first command is to write 1 in /proc/sys/net/ipv4/ip_forward. It is equivalent to this command:

echo 1 > /proc/net/ipv4/ip_forward
The second command is to apply all changes in file /etc/sysctl.conf.

Whatever you set in sysctl.conf will be applied every system restart. So that's important if you want to enable it permanently as in the case of a router. First command doesn't do that. You have to edit sysctl.conf to make it permanent because it will be read every system restart. Edit t…