Difference between revisions of "Linux Tools"

Latest revision as of 20:08, 23 July 2012

[edit] Linux Tutorials

• For beginners, skip tutorial 7: http://www.ee.surrey.ac.uk/Teaching/Unix/

[edit] vim tips and tricks

• http://www.cs.swarthmore.edu/help/vim/home.html
• http://jmcpherson.org/editing.html

[edit] ssh-keygen

To be able to ssh to another machine without needing to type your passwd:

Generate keys: $ ssh-keygen -t rsa -b 1024

Use the default file name and empty pass phrase for password less authentication. This will generate keys in

$ .ssh/id_rsa.pub

Then secure shell copy to another host as authorized_keys

$ scp ~/.ssh/id_rsa.pub <machine name>:~/.ssh/authorized_keys

Instructions copied from: http://pr.willowgarage.com/wiki/GB_ssh-keygen

Additional keys can be named authorized_keys2 or put below the existing keys in authorized_keys or authorized_keys2.

[edit] Imagemagick

handy tool to crop images etc.

1. convert -crop 700x500+550+200 8.png 8_cropped.png - crops an image to a size of 700x500 with an offset of 550, 200 from the top left.

[edit] combining, extracting pages etc. from PDF documents

• sudo apt-get install gs pdftk sam2p
• Extract pages from a pdf:
  • http://www.linuxjournal.com/content/tech-tip-extract-pages-pdf
  • pdftk A=full_document.pdf cat A1-7 output first_seven_pages.pdf
• Combine multiple pdfs:
  • gs -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=combinedpdf.pdf -dBATCH *.pdf
• Reduce the file size of a pdf:
  • http://www.ubuntugeek.com/ubuntu-tiphowto-reduce-adobe-acrobat-file-size-from-command-line.html
  • Advait found that the vanilla command on the website degraded the image quality by a lot.
    • One of the comments mentioned dropping the -dPDFSETTINGS=/screen option. This worked for Advait.
  • gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf
• converting pdf to grayscale:
  • gs -sOutputFile=gray.pdf -sDEVICE=pdfwrite -sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray -dCompatibilityLevel=1.4 -dNOPAUSE -dBATCH everyday_mechanics.pdf

[edit] command line tools: find, sed, rename

The find command is pretty nifty:

1. find all directories whose name does not contain svn: find . ! -path "*.svn*" -type d
2. remove .svn folders, e.g. after copying a directory which is a local copy of a subversion repository: rm -rvf `find . -name "*.svn"`
3. recursively remove all the .pycs: alias rmpyc='rm -vf *.pyc; rm -vf `find . -name *.pyc`'
4. remove the pesky .pycs from the repository: svn rm `find . -name "*.pyc"`
5. list all pkl files with the word grasp but not the word choose: find . -name '*grasp*.pkl' -and ! -name '*choose*.pkl'
6. avoid initial ./ in file name: find * -name "pull_trajec*.pkl"

So is sed:

1. replace update_path with load_manifest. (-i is doing an in-place replace, Advait believes): sed -i 's/update_path/load_manifest/' `find . -name "*.py"`
2. look at the insert_license.sh script in gt-ros-pkg for some more examples of using sed.

And rename:

1. Rename JPG to jpg for all the files in a folder: rename 's/JPG/jpg/' *

Use netcat to test ports

1. nc -l 1234
2. nc 127.0.0.1 1234

[edit] bash scripting

1. padding zeros before file or directory names: mkdir `printf "%03d %04d" 5 6`
2. counters in bash scripts: N=1 ... let N=$N+1
3. listing only the directory names: ls */ -d
4. http://tldp.org/LDP/abs/html/refcards.html

[edit] udev for persistent device naming

[edit] Steps in brief

• sudo lsusb -v >pre # with device being unplugged
• sudo lsusb -v >post # with device being plugged in
• diff pre post (or use meld for a nicer graphical tool for comparing files) # you can read the Serial Number on the line "iSerial" etc.
• Now edit the udev rules in /etc/udev/rules.d/10-ROBOT.rules
• sudo /etc/init.d/udev restart
• ls /dev/robot -- to check whether the devices appear.

[edit] Sample file

Here is a sample 10-ROBOT.rules file that we use on our robot.

BUS=="usb", KERNEL=="ttyUSB*", SYSFS{idVendor}=="0403", SYSFS{idProduct}=="6001", SYSFS{serial}=="A7003N1b", SYMLINK+="robot/servo0"
BUS=="usb", KERNEL=="ttyUSB*", SYSFS{idVendor}=="0403", SYSFS{idProduct}=="6001", SYSFS{serial}=="ftDXR6FS", SYMLINK+="robot/zenither" 

SUBSYSTEMS=="usb", KERNEL=="ttyACM*", PROGRAM="/home/advait/ros/pkgs/ros-pkg-trunk/stacks/laser_drivers/hokuyo_node/bin/getID /dev/ttyACM%n q",  ATTRS{manufacturer}=="Hokuyo Data Flex for USB", ATTRS{product}=="URG-Series USB Driver", SYMLINK+="robot/hokuyo_%c" 

BUS=="usb", SYSFS{idVendor}=="0403", SYSFS{idProduct}=="e729", SYSFS{serial}=="00000215", SYMLINK+="robot/segway_front"
BUS=="usb", SYSFS{idVendor}=="0403", SYSFS{idProduct}=="e729", SYSFS{serial}=="00000201", SYMLINK+="robot/segway_back" 

SUBSYSTEM!="usb", GOTO="robot_rules_end"
ACTION!="add", GOTO="robot_rules_end"
ATTRS{idVendor}=="0403", ATTRS{idProduct}=="e729", MODE="0660", GROUP="plugdev"
LABEL="robot_rules_end"

[edit] More information

• http://www.reactivated.net/writing_udev_rules.html#why
• detailed info about writing udev rules: http://www.reactivated.net/writing_udev_rules.html

[edit] Linux & Mac Hardware

• fix mac function keys in ubuntu: link