Posts Tagged tips

A little one-liner: rename to lowercase recursively

Here is my little one-liner, because I used it today and I find it fun:

for f in `find .` ; do mv $f `echo $f | tr '[A-Z]' '[a-z]'` ; done 

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Installing redmine 0.8 on intrepid (ubuntu 8.10)

I’ve successfully insalled redmine pretty much easily but I needed to find out what packages to install with apt, which one with gem, which version …
Here is my magic receipe to install it all:

apt-get update 
apt-get install subversion mysql-server rubygems rake pwgen
# next line generates a password for the database
export PASSWORD=`pwgen -nc 8 1`
gem install -v=2.1.2 rails
echo "CREATE DATABASE redmine  DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci ; GRANT ALL PRIVILEGES ON redmine.* TO 'redmine'@'localhost' IDENTIFIED BY '$PASSWORD' WITH GRANT OPTION; FLUSH PRIVILEGES" | mysql 
cd /opt/
svn export http://redmine.rubyforge.org/svn/branches/0.8-stable redmine-0.8
cd redmine-0.8/
cat <<EOF >> config/database.yml
production:
  adapter: mysql
  socket: /var/run/mysqld/mysqld.sock 
  database: redmine
  host: localhost
  username: redmine
  password: $PASSWORD
  encoding: utf8

EOF
rake db:migrate RAILS_ENV="production"
rake redmine:load_default_data RAILS_ENV="production"
apt-get remove pwgen subversion
RAILS_ENV="production" ./script/server  

And that’s it ! Redmine is running on port 3000.
I did this on an EC2 instance and it works like a charm (ami-7cfd1a15).
Maybe next article will discuss running redmine in mongrel or apache, and creating an init script for having redmine running on boot !

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Hostname and underscore

RFC 952 and RFC 1123 explains the rules for choosing a hostname. I noticed recently that a lot of admins (including me) are using underscores in hostnames, but this doesn’t follow RFCs. This can lead to strange behaviours, such as mail not delivered with an RFC compliant mail server to an MX that have underscores in its name …
I noticed that because the “hostname” command on linux can set the hostname of a system, but the command doesn’t accept underscores. So guys, don’t use underscores !

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MySQL “pretty printing”

I just discovered an apparently wide spread tip for mysql:


mysql> select 1, 2, 3, 4 ;
+---+---+---+---+
| 1 | 2 | 3 | 4 |
+---+---+---+---+
| 1 | 2 | 3 | 4 |
+---+---+---+---+
1 row in set (0.00 sec)


mysql> select 1, 2, 3, 4 \G;
*************************** 1. row ***************************
1: 1
2: 2
3: 3
4: 4
1 row in set (0.00 sec)

As you might have seen, the difference comes from the “\G” !

It’s very usefull when you select lot of columns that doesn’t fit the width of your terminal !
Shame on me I didn’t knew that before !

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web based bind zone generator

There a some web based bind zone generator, but searching for “zone generator” in google, I found a lot that aren’t working, refining my research didn’t helped me. I finally found one that does the stuff. It’s not optimal , but it work , and it’s there
Please, if you know of a better one, just let me know !

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Biggest file in a tree

There are plenty of solutions to find biggests files in a tree on unix.
I usually used
find . -type f -exec du -sk {} \; |sort -nrk1
until I found it too slow, on a really big partition with a lot of files. It’s slow because the -exec option of find forks for each file , and the du re-fetches the inode for every files (IIRC the inode should be in the buffer cash, the really expensive part is the forking).

Now I usually use this command which is really more efficient (depending essentially on number of files
find . -type f -ls |awk '{print "$7" "$11" }' | sort -nrk1

Conclusion: Fork is expensive 🙂

UPDATE:
As my friend nikoteen said in the comment of this post, there is a better solution:
find -ls | sort -k7
The thing is, unix people are (ohh, sorry, I am) used to use some commands with it’s usual argument for example, I often use: ls -lart, tar zcvf, netstat -atnup. And sort -nrk1 is one of that command I often use. That’s why I’m writing stupid commands with awk | sort rather than just writing a simple sort. So guys, use this command:
find -ls | sort -k7

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copying databases

Similarly to my last tip (copying directory with ssh and tar) , you can also copy databases. It’s pretty simple, here is my magic command:
mysqldump -ppassword db |ssh user@remote "cat - | mysql -u dbuser -ppassword db"

Here, you can also gzip or bzip2 the input, and it should be very efficient, because mysqldump output is pure ascii with sql, gzip and bzip2 will easily find good pattern for compression.

Also, as usual, using my.cnf files, you don’t need -ppassword parameters.

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