Linux Admin

/etc/sudoers

The man page gives a complete but unclear description of the file specification. Here a simplified but complete version:

First the description of possible entries in the file:

# Alias
'User_Alias'  NAME '=' User...         (':' NAME '=' User...        )*  |
'Runas_Alias' NAME '=' Runas_Member... (':' NAME '=' Runas_Member...)*  |
'Host_Alias'  NAME '=' Host...         (':' NAME '=' Host...        )*  |
'Cmnd_Alias'  NAME '=' Cmnd...         (':' NAME '=' Cmnd...        )*

#Default_Entry
'Defaults' ('@' Host... | ':' User... | '!' Cmnd... | '>' Runas_Member...)? Parameter...

#User_Spec
User... Host... '=' Cmnd_Spec...       (':' Host... '=' Cmnd_Spec...)*

Now the description of the syntactical elements:

identifier... ::= identifier (',' identifier)*

NAME          ::= [A-Z]([a-z][A-Z][0-9]_)*

User /
Runas_Member  ::= '!'* ( username | '#'uid | '%'group | '+'netgroup | Alias | 'ALL' )

Host          ::= '!'* ( hostname | ip_addr | network(/netmask)? | '+'netgroup | Alias| 'ALL' )

Cmnd          ::= '!'* ( command filename (args | '""')? | directory | "sudoedit" | Alias | 'ALL' )

Parameter     ::= Parameter '=' Value | Parameter '+=' Value | Parameter '-=' Value | '!'* Parameter

Cmnd_Spec     ::= ('(' Runas_Member...? (':' ...? ')')? ('NOPASSWD:'|'PASSWD:'|'NOEXEC:'|'EXEC:'|'SETENV:'|'NOSETENV:')* Cmnd

File Systems

Reiserfs

• For better performance, use mount switch noatime,notail (see [1])

udev & devfs

Reference: [2]

This chapter is about the devices in /dev. Since kernel 2.6, the content of this directory is generated by udev rules.

These rules are located at:

• /lib/udev/rules.d
• /etc/udev/rules.d (these can be customized)

Use udevadm to get information on a given device:

udevadm info -q path -n /dev/sda2                                     # To get the path to the device /dev/sda2
udevadm info -q -n /dev/sda2                                          # To get all the attributes of device /dev/sda2
udevadm info -a -p $(udevadm info -q path -n /dev/sda2)               # Same as above
udevadm test $(udevadm info -q path -n /dev/sda2) 2>&1 | grep OWNER   # Test the effect of a new rule on device /dev/sda2

Managing Alternatives

For instance, to define the default cursor-theme, use update-alternatives:

sudo update-alternatives --config x-cursor-theme