Linux FAQ
These are some basic Linux commands and techniques for new to Linux users. More complete information can be found on the web or by using the man pages.
1. Automatic Login
When you install LinuxCNC with the Ubuntu LiveCD the default is to have to log in each time you turn the computer on. To enable automatic login go to System > Administration > Login Window. If it is a fresh install the Login Window might take a second or three to pop up. You will have to have your password that you used for the install to gain access to the Login Window Preferences window. In the Security tab check off Enable Automatic Login and pick a user name from the list (that would be you).
2. Automatic Startup
To have LinuxCNC start automatically with your config after turning on the computer go to System > Preferences > Sessions > Startup Applications, click Add. Browse to your config and select the .ini file. When the file picker dialog closes, add linuxcnc and a space in front of the path to your .ini file.
Example:
linuxcnc /home/mill/linuxcnc/config/mill/mill.ini
3. Man Pages
A man page (short for manual page) is a form of software documentation usually found on a Unix or Unix-like operating system like Linux.
To view a man page open up a terminal window by going to Applications > Accessories > Terminal. Some Linux desktops support Ctrl + Alt + t to open a terminal. For example if you wanted to find out something about the find command in the terminal window type:
man find
Use the Page Up and Page Down keys to view the man page and the Q key to quit viewing.
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Note
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Viewing the man page from the terminal may not get the expeced man page. For example if you type in man abs you will get the C abs not the LinuxCNC abs. It is best to view the LinuxCNC man pages in the HTML documents. |
4. List Modules
Sometimes when troubleshooting you need to get a list of modules that are loaded. In a terminal window type:
lsmod
If you want to send the output from lsmod to a text file in a terminal window type:
lsmod > mymod.txt
The resulting text file will be located in the home directory if you did not change directories when you opened up the terminal window and it will be named mymod.txt or what ever you named it.
5. Editing a Root File
When you open the file browser and you see the Owner of the file is root you must do extra steps to edit that file. Editing some root files can have bad results. Be careful when editing root files. Generally, you can open and view most root files, but they will open in read only mode.
5.1. The Command Line Way
Open up Applications > Accessories > Terminal.
In the terminal window type
sudo gedit
Open the file with File > Open > Edit
5.2. The GUI Way
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Right click on the desktop and select Create Launcher
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Type a name in like sudo edit
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Type gksudo "gnome-open %u" as the command and save the launcher to your desktop
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Drag a file onto your launcher to open and edit
5.3. Root Access
In Ubuntu you can become root by typing in "sudo -i" in a terminal window then typing in your password. Be careful, because you can really foul things up as root if you don’t know what you’re doing.
6. Terminal Commands
6.1. Working Directory
To find out the path to the present working directory in the terminal window type:
pwd
6.2. Changing Directories
To move up one level in the terminal window type:
cd ..
To move up two levels in the terminal window type:
cd ../..
To move down to the linuxcnc/configs subdirectory in the terminal window type:
cd linuxcnc/configs
6.3. Listing files in a directory
To view a list of all the files and subdirectories in the terminal window type:
dir
or
ls
6.4. Finding a File
The find command can be a bit confusing to a new Linux user. The basic syntax is:
find starting-directory parameters actions
For example to find all the .ini files in your linuxcnc directory you
first need to use the pwd command to find out the directory.
Open a new terminal window and type:
pwd
And pwd might return the following result:
/home/joe
With this information put the command together like this:
find /home/joe/linuxcnc -name \*.ini -print
The -name is the name of the file your looking for and the -print tells it to print out the result to the terminal window. The \*.ini tells find to return all files that have the .ini extension. The backslash is needed to escape the shell meta-characters. See the find man page for more information on find.
6.5. Searching for Text
grep -irl 'text to search for' *
This will find all the files that contain the text to search for in the current directory and all the subdirectories below it, while ignoring the case. The -i is for ignore case and the -r is for recursive (include all subdirectories in the search). The -l option will return a list of the file names, if you leave the -l off you will also get the text where each occourance of the "text to search for" is found. The * is a wild card for search all files. See the grep man page for more information.
6.6. Diagnostic Messages
To view the diagnostic messages use "dmesg" from the command window. To save the diagnostic messages to a file use the redirection operator >, like this:
dmesg > bootmsg.txt
The contents of this file can be copied and pasted on line to share with people trying to help you diagnose your problem.
To clear the message buffer type this:
sudo dmesg -c
This can be helpful to do just before launching LinuxCNC, so that there will only be a record of information related to the current launch of LinuxCNC.
To find the built in parallel port address use grep to filter the information out of dmesg.
After boot up open a terminal and type:
dmesg|grep parport
7. Convenience Items
7.1. Terminal Launcher
If you want to add a terminal launcher to the panel bar on top of the screen you typically can right click on the panel at the top of the screen and select "Add to Panel". Select Custom Application Launcher and Add. Give it a name and put gnome-terminal in the command box.
8. Hardware Problems
8.1. Hardware Info
To find out what hardware is connected to your motherboard in a terminal window type:
lspci -v
8.2. Monitor Resolution
During installation Ubuntu attempts to detect the monitor settings. If this fails you are left with a generic monitor with a maximum resolution of 800x600.
Instructions for fixing this are located here:
9. Paths
Relative paths are based on the startup directory which is the directory containing the ini file. Using relative paths can facilitate relocation of configurations but requires a good understanding of linux path specifiers.
./f0 is the same as f0, e.g., a file named f0 in the startup directory ../f1 refers to a file f1 in the parent directory ../../f2 refers to a file f2 in the parent of the parent directory ../../../f3 etc.