Linux Advanced
Advanced file permissions Linux
Sticky Bit
The sticky bit is set on a directory as a way to prevent users from removing files that they do not own. It is represented by the t over the x position on the other octal as in -rwxrwxrwt or -rwxrwxrwT when the x bit is not set on other.
You can set it by using chmod 1775 or chmod +t
Setgid bit on directory
The setuid can be set on a directory to ensure that all files inside the directory are owned by the group owner of the directory. It is represented by the s over the x position on the group octal as in -rwxrwsrwx or -rwxrwSrwx when the x bit is not set on group.
You can set it by using chmod 2775 or chmod g+s
Setgid and Setuid on files
When setuid is set on a file it causes the file to be executed by the file owner instead of the executing owner and when setgid is set on a file it causes the file to be executed by the file group instead of the executing owner.
To change permissions on all directories in a folder cd into it and run
sudo find . -type d -exec chmod xxxx {} \ ;
or for files
sudo find . -type f -exec chmod xxxx {} \ ;
where xxxx is your octals like 2755 or u=rwx,g=rx,o=r for example chmod 2755 or chmod u=rwx,g=rx,o=r
Linux change permission on all directories within a directory not recursively
You can use the find command from terminal. CD info the directory you wnat to run the command in.
List the folder first to see that we have the correct ones
sudo find . -maxdepth 1 -type d -ls
If we have a list of the directories we want then we can run
sudo find . -maxdepth 1 -type d -exec chmod 755 {} \;
To change the permissions on all directories or files in a certain path linux
First we have to use find command to look for either directories of files and then we use the exec command on our find.
To change the permissions on all directories in a certain path
$ sudo find /path/you/want/to/search -type d -exec chmod 775 {} +
To change the permissions on all files in a certain path
$ sudo find /path/you/want/to/search -type f -exec chmod 775 {} +
To Know what the chmod 775 does go here
Change extension of file type in multiple files in Linux
If your interested in converting all higher case "JPG" extensions to lower case "jpg" You could use the command line utility rename like so. CD into directory you want to change. Then
rename -n 's/\.JPG$/\.jpg/' *
Use -n option to test what will be changed, then when you happy with results use without like so
rename 's/\.JPG$/\.jpg/' *
List directory size one folder deep in human-readable form Linux
To list all the directories in a folder by size without giving all subfolders, a nice clear list with no clutter use
$ du --max-depth 1 -h
du = estimate file space usage
--max-depth 1 = only go 1 deep in the tree
-h = human-readable
For example
/var$ sudo du --max-depth 1 -h
21M ./log
4.3M ./backups
4.0K ./mail
5.5M ./crash
8.0K ./www
588M ./cache
4.0K ./tmp
56K ./spool
4.0K ./local
4.0K ./opt
551M ./lib
1.2G .
It also totals the whole directory at the end. Pretty cool.
Add text to .avi or mpeg4 video files on Ubuntu 12.04
In order to add text to a video file first we need to make sure we have all the editing tools and codecs
sudo apt-get install ubuntu-restricted-extras
sudo apt-get install ffmpeg x264
sudo apt-get install frei0r-plugins mjpegtools
Once all these are installed we can add text by running the command below
sudo ffmpeg -i /media/Verbatim/ty/new/130251.mp4 -vf drawtext="fontfile=/usr/share/fonts/truetype/freefont/FreeSans.ttf: text='Your own text to add here':fontcolor=white@1.0:fontsize=70:x=300: y=600" -y 130251_num8.mp4
- where -i specifies the input file
- -vf specifies what you want to do to the file
- drawtext adds the text Your own text to add here with a colour of white fontsize 70 and at the x y cooridainates 300 600
- output file name is 130251_num8
- output file format is mp4
The code above will let ffmpeg choose the audio and video codecs which most times is not what you want because it can decrease the quality of the video. In order to select the codecs to apply, use the code below.
sudo ffmpeg -i /home/drupalpro/Desktop/ty/130257.mp4 -vf drawtext="fontfile=/usr/share/fonts/truetype/freefont/FreeSans.ttf: text='130257':fontcolor=red@1.0:fontsize=70:x=350: y=650" -vcodec libx264 -crf 18 -acodec copy 130257.mp4
- only change is -vcodev libx264 which select the h.264 codec which is the best
- -crt which sets the quality (high is bad and low is good) -crt 16 is supposed to be visually lossless to the human eye but -crt 0 is true lossless and will take a long time to encode
- and -acodec copy which just copies the original
FFmpeg also alows yout to sync your audio to video.
$ ffmpeg -i input.avi -itsoffset 0.2 -i input.avi -map 0:0 -map 1:1 -acodec copy -vcodec copy synced.avi
Check out http://alien.slackbook.org/blog/fixing-audio-sync-with-ffmpeg/ for a detailed explanation.
Restart Networking Ubuntu Linux
If using ifconfig eth0 down and up on ubuntu it wont renew the IP from the DHCP server. For this we need to restart the network manager.
To restart the networking service in ubuntu in order to get new IP from DHCP
sudo service network-manager stop
sudo service network-manager start
Linux Permissions
Linux permissions are set for three groups on each file or folder. The three groups are Owner, Group and World. If I open a terminal and type;
ls -la
drwxr-xr-x 44 drupalpro drupalpro 4096 Mar 27 18:03 .
drwxr-xr-x 4 root root 4096 Jun 17 2012 ..
drwx------ 3 drupalpro drupalpro 4096 Jun 22 2012 .adobe
drwxr-xr-x 8 drupalpro drupalpro 4096 Jun 22 2012 Aptana_Studio_3
-rw-rw-r-- 1 drupalpro drupalpro 5188 Jun 22 2012 .bash_aliases
-rw-rw-r-- 1 drupalpro drupalpro 16168 Mar 27 19:00 .bash_eternal_history
-rw------- 1 drupalpro drupalpro 6935 Mar 27 17:33 .bash_history
-rw-r--r-- 1 drupalpro drupalpro 220 Jun 17 2012 .bash_logout
-rw-r--r-- 1 drupalpro drupalpro 3486 Jun 17 2012 .bashrc
drwx------ 12 drupalpro drupalpro 4096 Mar 27 16:31 .cache
drwxr-xr-x 7 drupalpro drupalpro 4096 Mar 12 07:09 commerce_kickstart
drwxrwxr-x 7 drupalpro drupalpro 4096 Mar 26 16:40 commons
So looking at the last one on the list we see the first part of the listing drwxrwxr-x give the permissions for the directory commons. The permissions work from left to right in this order ( Owner, Group and World). What this tells us is that its a directory (drwxrwxr-x) and that the owner has rwx permissions (read,write,execute), the group has rwx permissons (read,write,execute) and the world has r-x (read,execute).
| Octal | Decimal | Permission | |
| 000 | 0 (0+0+0) | no permission | --- |
| 001 | 1 (0+0+1) | execute | --x |
| 010 | 2 (0+2+0) | write | -w- |
| 011 | 3 (0+2+1 | write and execute | -wx |
| 100 | 4 (4+0+0) | read | r-- |
| 101 | 5 (4+0+1) | read and execute | r-x |
| 110 | 6 (4+2+0) | read and write | rw- |
| 111 | 7 (4+2+1) | read and write and execuute | rwx |
Create a Concateneted Volume
Initialize the disk or partition for use by the Logical Volume Manager LVM
pvcreate /dev/sdb1 /dev/sdb2 /dev/sdb3 /dev/sdb4
pvs
pvdisplay
Create a volume group
vgcreate myvg /dev/sdb1 /dev/sdb2
vgdisplay
Create a logical volume in an existing volume group
lvcreate --size 1g myvg (creates /dev/myvg/lv01
lvs
lvdisplay
Build the file system ext4 on our new logical volume /dev/myvg/lv01
mkfs -t ext4 /dev/myvg/lv01
Software Packages
To list all of the packages installed on you system
rpm -qa
Different flavors of linux have different package managers that do a lot of the backgroung work like installing dependencies.
SuSe uses zypper
To install a package named nmap
zypper in nmap
To search for a package using zypper
zypper se nmap
Where is the package installed
which nmap
/usr/bin/nmap
What version of the package is installed
rpm -qf /usr/bin/nmap