Archive for October, 2008
October 28, 2008 at 2:21 pm
· Filed under Uncategorized ·Tagged backup, database, databases, dba, mysql, mysqldump, script, scripting, shell script, shell scripting, sql, sysadmin, system, system administration, tips and tricks
Today I encountered a problem: I needed to restore a single table from a database mysqldump.
Usually you cat the-mysqldump.sql |mysql the_database so you’re only able to restore the full database. I didn’t find any mysqldump option to extract a single table from a full database dump, so I’ve come up with this (minimal) shell script:
#!/bin/sh
extract_table(){
TABLE=$1
DUMPFILE=$2
grepstr="/*!40000 ALTER TABLE \`$TABLE\`"
lines=`grep -n "$grepstr" $DUMPFILE |cut -d":" -f1`
lines=`echo $lines|sed 's/\ /,/' `
echo "LOCK TABLES \`$TABLE\` WRITE;"
sed -n "$lines p" $DUMPFILE
echo "UNLOCK TABLES;"
}
extract_table $1 $2
Use it like this:
./this-script.sh table-to-extract dumfile-for-extract |mysql the_database (use the |mysql after you have checked the content).
Be carefull, this script is minimalistic:
- It doesn’t check if the file exist and is really a mysqldump file
- It doesn’t check if the table to extract exists
- It doesn’t work if disable-keys is set to false in mysqldump
- It doesn’t have a usage() function
If some people request it, I’ll write all these features, but as usual, I wanted to come up with a solution I could already use one hour a ago, and I’m spending time to write this script, let’s do it the faster I can !
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October 28, 2008 at 1:31 pm
· Filed under Uncategorized ·Tagged linux, script, scripting, shell, shell script, shell scripting, tips and tricks, unix
Let’s say you want to extract a part of a file, for example from line 12 to 20.
I’ve come up with two solutions:
head -n20 |tail -n8
You take the n’th first line where n is the last line you want, then you go backward by the total line number you want to have, that is: 20-12=8
- A nicer solution which is straightforward (use the right tools guys !):
sed -n '12,20p'
You need the -n option, so that the input is not printed to the output, than give sed an expression (within quotes), the expression is the first line, a coma, the last line, and the “p” instruction which means print.
This solution doesn’t need you to calculate the number of lines you will get, I find it nicer !
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October 22, 2008 at 10:54 am
· Filed under Uncategorized ·Tagged linux, mail, network, networking, smtp, ssmtp, system, unix
Unix systems often needs a local mailer, but configuring and maintaining a mailer on each system is a timeloss.
You might have a gmail or google apps account. If it’s the case, you can easily configure a mailer on your systems which uses your gmail or google apps. To do so, I’ve used ssmtp and put this in /etc/ssmtp/ssmtp.conf:
root=postmaster
mailhub=smtp.gmail.com:587
AuthUser=your-mail@yourdomain.com
AuthPass=aStr4angeP45s
UseSTARTTLS=YES
hostname=the-hostname
That’s it, simple, effective, working …
To improve the things, maybe, we can use an IP address of the smtp server, so that if our DNS server doesn’t work, we still have mail on the system, but this has a drawback, if the server for which you gave an ip address changes or temporarly doesn’t work, you don’t have mail anymore.
ssmtp doesn’t seem to be able to have several mailhubs !
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October 16, 2008 at 9:53 am
· Filed under Uncategorized ·Tagged admin, commands, linux, process, shell, sysadmin, system, system administration, unix
I just discovered the watch command, it can be useful !
If you don’t know watch, it does what you would do like this:
while true ; do "your command" ; sleep 1 ; clear ; done
that is, it executes in a while loop the same command , with a sleep so that it doesn’t overkill your cpu.
It also has nice parameters, for exemple --differences that can only show the differences between current and last run.
“your command” could be a du or a df , --differences could be useful when used with an ls to monitor a directory …
Read the manpage and have fun !
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October 13, 2008 at 5:08 pm
· Filed under Uncategorized ·Tagged backup, dd, disk, dump, network, networking, pipe, ssh, system
If you want to dump a disk to a disk image you will use for example:
dd if=/dev/hdx1 of=/tmp/disk.img
and then, you will probably copy this disk image to another machine. The thing is, if you have low disk space than the size of /dev/hdx1 on your machine, you won’t be able to dump the disk to transfer it to the other machine.
There is a solution that I use, as usually with, ssh and pipe:
ssh hostname "dd if=/dev/hdx1" |dd of=/tmp/disk.img
on the machine receiving the image or
dd if=/dev/hdx1 |ssh hostname "dd of=/tmp/disk.img"
on the machine sending the image, so the content of the disk is directly transmitted through ssh !
That’s it !
Maybe you can tune the blocksize of the dd command so the troughput is better, maybe a futur article on that
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October 11, 2008 at 11:22 am
· Filed under Uncategorized ·Tagged browser, ip, ipv6, network, networking, scp, ssh, system, url, urls, web
URLs are written like this: protocol://host-or-address:port/path-or-function
What happens with ipv6 is that addresses contains colons (“:”) , so how do you specify the port number in your web browser ? The same happens when you do an scp: you usually do scp user@host:path/to/file /local/path, how can you differenciate the host part and the path which are also seperated with a colon ?
The answer is: USE BRACKETS !
an ipv6 url can be written like this:
http://[fe80::abcd:abcd:abcd:abcd]:8080/index.html
Also, a scp command with ipv6 addresses can be like this:
scp user@[fe80::abcd:abcd:abcd:abcd]:/etc/resolv.conf /tmp
I hope it’s usefull !
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October 6, 2008 at 4:12 pm
· Filed under Uncategorized ·Tagged icmp, linux, mac, network, osx, ping, scan, script, scripting, scripts, shell, subnet, system
Today I logged in a machine I don’t want to install anything on it, but I wanted to find a machine in its network.
I came up with the little shell script that scans the subnet:
CURR=1
SUBNET="192.168.0"
while [ $CURR -lt 255 ] ; do
ping -c1 -t1 $SUBNET.$CURR 2>&1 >/dev/null
if [ "$?" -eq "0" ]; then
echo "$SUBNET.$CURR"
fi
let CURR=$CURR+1
done
This script is suboptimal but it does the stuff: It uses ping with a timeout of 1 sec, so If no machine is up, the script takes around 255 seconds to scan the subnet, it doesn’t list the machines that doesn’t reply to ping and so on … but as I said it , it does the stuff.
I tested this script in Linux and OSX.
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