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# List all users

cat /etc/passwd | cut -d: -f1

# List all non-system users

awk -F: '{if ($3>=500 && $3<=1000) print $1}' /etc/passwd

 

# List all groups

cat /etc/group | cut -d: -f1

 

# Add an existing user to a group - http://www.cyberciti.biz/faq/howto-linux-add-user-to-group/

# usermod -a -G ftp tony

 

 

 

# Chmod usage - http://en.wikipedia.org/wiki/Chmod

chmod [options] mode[,mode] file1 [file2 ...]

 

# Modes

u       user    the owner of the file

g       group   users who are members of the file's group

o       others  users who are not the owner of the file or members of the group

a       all     all three of the above, is the same as ugo

 

Operator        Description

+       adds the specified modes to the specified classes

-       removes the specified modes from the specified classes

=       the modes specified are to be made the exact modes for the specified classes

 

Mode    Name    Description

r       read    read a file or list a directory's contents

w       write   write to a file or directory

x       execute execute a file or recurse a directory tree

X       special execute which is not a permission in itself but rather can be used instead of x. It applies execute permissions to directories regardless of their current permissions and applies execute permissions to a file which already has at least 1 execute permission bit already set (either user, group or other). It is only really useful when used with '+' and usually in combination with the -R option for giving group or other access to a big directory tree without setting execute permission on normal files (such as text files), which would normally happen if you just used "chmod -R a+rx .", whereas with 'X' you can do "chmod -R a+rX ." instead

s       setuid/gid      details in Special modes section

t       sticky  details in Special modes section