Libre Things

Several desktop environments (Gnome, KDE) automatically start an SSH agent at startup. However, you have to think of running ssh-add before connecting to a server.

Waiting for automatic ssh-add in OpenSSH, you can add this to your .bashrc:

ssh-add -l >/dev/null || alias ssh='ssh-add -l >/dev/null || ssh-add && unalias ssh; ssh'

The alias is created only if the identity is not added, and the alias destroys itself once run.

This way the regular ssh command is used after the identity has been added.

http://superuser.com/questions/325662/how-to-make-ssh-agent-automatically-add-the-key-on-demand/471640#471640

I'm looking for a new laptop. My old T42p Thinkpad is becoming old. I'm looking for a laptop with a good screen...

However... finding a laptop with a resolution similar to my T42p is impossible on today's market. The T42p has been released for more than 8 years now!! When I'm speaking resolution, I mean pixel density in PPI. My resolution is of 1400x1050 for 14.1 inches, which is good! it gives a density of 124 PPI.

Nowadays, all laptops have the same unique 1366x768 resolution. The last thinkpad X1 from Lenovo with 13.3 inches is only 118 PPI.

It's revolting! I want my pixels!

Apparently I'm not the only one in this situation...

• http://10rem.net/blog/2010/04/22/rant-hdtv-has-ruined-the-lcd-display-market-or-i-want-my-pixels-and-dpi-now
• http://boards.straightdope.com/sdmb/showthread.php?t=421095
• http://www.tabletpcbuzz.com/showthread.php?1624-Pixel-Density-Hostage-Crisis!&s=32e284cd59d44346c32f2471636389f2
• http://www.tomshardware.co.uk/forum/59742-29-higher-pixel-pitch

It's sad. Maybe it will be better in the future... with our cell phones screens having far better resolutions...

Other usefull links :

• http://en.wikipedia.org/wiki/Pixel_density
• PPI Calculator

Small contribution to CyanogenMod wiki

Physical keyboard is changed to QWERTY after CyanogenMod 6 flash. if your HTC Dream has an AZERTY keyboard:

• Download http://www.mon-cobaye.net/vrac/modif.zip (see SPF forum post)
• Copy trout-keypad-v3.kl and azerty.kcm.bin to your sdcard
• Then run the commands:

adb remount
adb shell
cat /sdcard/trout-keypad-v3.kl > /system/usr/keylayout/trout-keypad-v3.kl
cat /sdcard/azerty.kcm.bin > /system/usr/keychars/trout-keypad-v3.kcm.bin

• Then reboot your phone

Some doc: http://source.android.com/tech/input/key-layout-files.html

Here is the little sh script I made to do that. The LOAD DATA INFILE command exists but is not capable of creating the table structure.

#!/bin/sh

MYSQL_ARGS="--defaults-file=/etc/mysql/debian.cnf"
DB="mbctest"
DELIM=";"

CSV="$1"
TABLE="$2"

[ "$CSV" = "" -o "$TABLE" = "" ] && echo "Syntax: $0 csvfile tablename" && exit 1

FIELDS=$(head -1 "$CSV" | sed -e 's/'$DELIM'/` varchar(255),\n`/g' -e 's/\r//g')
FIELDS='`'"$FIELDS"'` varchar(255)'

#echo "$FIELDS" && exit

mysql $MYSQL_ARGS $DB -e "
DROP TABLE IF EXISTS $TABLE;
CREATE TABLE $TABLE ($FIELDS);

LOAD DATA INFILE '$(pwd)/$CSV' INTO TABLE $TABLE
FIELDS TERMINATED BY '$DELIM'
IGNORE 1 LINES
;
"

http://dev.mysql.com/doc/refman/5.1/en/load-data.html

(See comment: "Posted by John Swapceinski on September 5 2011 5:33am")

Here are some lines I'm using to backup my MySQL databases on my Debian server:

#!/bin/sh
# This will dump all your databases

DATE=$(date +%Y%m%d%H%M)

for DB in $(echo "show databases" | mysql --defaults-file=/etc/mysql/debian.cnf -N)
do
        mysqldump --defaults-file=/etc/mysql/debian.cnf $DB > /backup/mysql/${DB}_${DATE}.sql

        gzip /backup/mysql/${DB}_${DATE}.sql
done

# purge old dumps
find /backup/mysql/ -name "*.sql*" -mtime +8 -exec rm -vf {} \;

You can run it in a cron:

11 1 * * * /usr/local/bin/mysqldump.sh > /tmp/mysqldump.log

This way any error displayed by the script will be sent by mail to the root user (mail address in /etc/aliases).

If you are not under Debian and there is no password file in /etc/mysql, you should create such file.

You have 2 systems and you want to set up a secure backup with rsync + SSH of one system to the other.

Very simply, you can use:

backup.example.com# rsync -avz --numeric-ids --delete root@myserver.example.com:/path/ /backup/myserver/

To do the backup, you have to be root on the remote server, because some files are only root readable.

Problem: you will allow backup.example.com to do anything on myserver.example.com, where just read only access on the directory is sufficient.

To solve it, you can use the command="" directive in the authorized_keys file to filter the command.

To find this command, start rsync adding the -e'ssh -v' option:

rsync -avz -e'ssh -v' --numeric-ids --delete root@myserver.example.com:/path/ /backup/myserver/ 2>&1 | grep "Sending command"

You get a result like:

debug1: Sending command: rsync --server --sender -vlogDtprze.iLsf --numeric-ids . /path/

Now, just add the command before the key in /root/.ssh/authorized_keys:

command="rsync --server --sender -vlogDtprze.iLsf --numeric-ids . /path/" ssh-rsa AAAAB3NzaC1in2EAAAABIwAAABio......

And for even more security, you can add an IP filter, and other options:

from="backup.example.com",command="rsync --server --sender -vlogDtprze.iLsf --numeric-ids . /path/",no-agent-forwarding,no-port-forwarding,no-pty,no-user-rc,no-X11-forwarding ssh-rsa AAAAB3NzaC1in2EAAAABIwAAABio......

Now try to open a ssh shell on the remote server.. and try some unauthorized rsync commands...

Notes:

• Beware that if you change rsync command options, change also the authorized_keys file.
• No need for complex chroot anymore. Forget my previous article: /post/SFTP-chroot-rsync

See also:

• man ssh #/AUTHORIZED_KEYS FILE FORMAT
• man rsync
• view /usr/share/doc/rsync/scripts/rrsync.gz (restricted rsync, allows you to manage allowed options precisely)

I discovered Clementine some time ago.

There is not any package for Ubuntu or Debian, but the official site gives you a .deb for your favorite Ubuntu version. And you'll also find Mac OS X and Windows versions...

A small click on the good .deb file for your Ubuntu distro and it should install.

I tested tons of players (Amarok, Rythmbox, old XMMS, Exaile, Listen, Totem...).

Clementine is based on Amarok, it's far simpler and integrates very well in Gnome desktop using Qt4 librairies.

I'm happy to know this software and I recommend it to you.

For the Bizou php gallery, I looked for different ways of preloading next image in "view" mode (example).

With Firefox it's very simple. Just use the following element and the browser will preload your contents. Contents are preloaded in background, once the whole current page is loaded.

<link rel="prefetch" href="/images/nextimage.jpg" />

Problem: only Firefox supports this currently. Note: a ticket is opened about this in the Chromium project.

For other browsers, use some Javascript triggered by the window.onload event:

<script type="text/javascript">
window.onload = function() {
    // for images
    var im = new Image();
    im.src = '/images/nextimage.jpg';
    // and for other content
    var req = new XMLHttpRequest();
    req.open('GET', 'nextpage.php', false);
    req.send(null);
};
</script>

Beware of HTTP cache headers sent by the server to the browser. To preload correctly PHP pages, make your script send an Expires header:

header('Expires: '.gmdate('D, d M Y H:i:s \G\M\T', time() + 3600));

Then, for a simple browser detection from your PHP script:

<?php if (strpos($_SERVER['HTTP_USER_AGENT'], 'Firefox') !== false) { ?>
<link rel="prefetch" href="nextpage.php" />
 
<?php } else { ?>
<script type="text/javascript">
window.onload = function() {
    var req = new XMLHttpRequest();
    req.open('GET', 'nextpage.php', false);
    req.send(null);
};
</script>
<?php } ?>

Links :

• https://developer.mozilla.org/en/Link_prefetching_FAQ
• http://www.4thkingdom.com/public/computers/789073-web-site-speed-prefetching-images-css/view-post.html (using jQuery)
• http://orip.org/2009/03/prefetching-javascript-or-anything-with.html (using jQuery)
• commit sur Bizou

Finding a good solution for sharing files between Linux users is a nightmare.

If using a unique UID is not a problem, it's the most simple solution. All clients access files with the same UID. This way you cannot know who does what, and users cannot fine tune access rights.

The problem: default umask is ALWAYS 0022, so that any created file will get rw– r–– r–– permissions. Only the owner can write. Nobody else. To share files, a group must have write access.

You can change the umask. For command line, you set it in .bashrc or .profile, or /etc/profile for all users. For a SFTP share, you can set it with a trick. For Apache HTTP server, you can set it with /etc/apache2/envvars under Debian.

If file sharing is only done via on service, changing umask is simple, otherwise it's not that easy. And even if you change umask for all services, nothing is perfect: for example it doesn't work with Nautilus and SFTP. Some clients drop files and issue a chmod right after: the hell. You can also try the power of POSIX ACL to force permissions. But problems still remain with some clients.

And for the umask, maybe you don't want all files to be dropped group writable. Maybe you want more granularity on permissions.

So I abandonned the idea of fixing the problem at the source in favor of some trick AFTER file creation. The most simple solution is the cron task: every X minutes, run chmod -R g+w on the directory. This way permissions are not fixed immediately, but asynchronously. And it adds a (very) little more load to your system.

My solution uses inotify to listen for file changes and force permissions when files are created:

aptitude install inotify-tools

And the magical command:

inotifywait -mrq -e CREATE --format %w%f /tmp/mytest/ | while read FILE; do chmod g=u "$FILE"; done

UPDATE 2010-10-30 To support spaces at the end of filenames, and backslashes, use:

inotifywait -mrq -e CREATE --format %w%f /tmp/mytest/ | while IFS= read -r FILE; do chmod g=u "$FILE"; done

Thanks to vitoreiji (see comments)

inotifywait listens for events in the /tmp/mytest directory. When a file is created, it's displayed on standard output. Then each fileline is read by the while loop and permissions are changed. g=u gives the group the user's permissions (with g+w, if the user drops a file with rw– ––– –––, permissions will be rw– –w– –––).

You can now test file/directory creation and copy. mkdir -p a/b/c/d/e shoud also work.

Finally, add it in a boot script:

vi /usr/local/bin/inotifywait.sh && chmod +x /usr/local/bin/inotifywait.sh
#!/bin/sh
# Take the directory name as argument

inotifywait -mrq -e CREATE --format %w%f "$1" | while read FILE
do
	chmod g=u "$FILE"
done

vi /etc/init.d/inotifywait.sh && chmod +x /etc/init.d/inotifywait.sh
#! /bin/sh

case "$1" in
  start|"")

	rm -f /tmp/inotifywait.log
	/usr/local/bin/inotifywait.sh /path/to/dir/ >/tmp/inotifywait.log 2>&1 &
	
	;;
  restart|reload|force-reload)
	echo "Error: argument '$1' not supported" >&2
	exit 3
	;;
  stop)
	# killall inotifywait ???
	;;
  *)
	echo "Usage: inotifywait.sh [start|stop]" >&2
	exit 3
	;;
esac

:

(Debian way)

update-rc.d inotifywait.sh defaults

Note: a drawback: there is a limit on the number of tracked files. See -r option in man inotifywait.

Then the final touch in order for the new files to be created with the same group as their parent: setgid bit for all directories.

find /path/to/dir -type d -exec chmod g+s {} \;

Links:

• man inotifywait
• inotify-tools
• http://en.wikipedia.org/wiki/Inotify