Introduction to Bio-Linux

Changing permissions on files and directories
The command to change permissions is chmod. You have to specify who you are modifying the permissions of,
what the new permissions are, and what file or directory to act on.
The format of the chmod command is:
who can take the value(s):
chmod who ± permissions filename
u
g
o
a
means user and refers to the owner of the file
means group, and refers to the group the file belongs to
means others, everyone on your systems apart from those above
means all three, i.e. user, group and others
Permissions can be:
r
w
x
means read permission
means write permission
means execute permission
So, for example, to give read permission to someone in the same group for a file called
“filename” in ~/intro_pract.
chmod g+r ~
gives permission to people in my group to read my home directory
chmod g+rx ~/intro_pract give permission to people in the group to list files in the intro_pract directory
chmod g+r ~/intro_pract/myfile give permission to people in the group to read the file
myfile (assuming they already have permission to “see” into the intro_pract directory).
A very basic way to stop a process
Sometimes a command or program goes on too long, or is obviously doing something you did not plan. If it is not
a situation where there is an obvious way (e.g. a menu option) to stop the program running, try using Control-c.
i.e. the Control key and c-key at the same time.
Logging out of a session
To logout, you can choose the option logout under the System menu.
Please do this at the end of the day – but not now.
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