CS199_Week_3 Flashcards
At a low level, users are represented by an integer called…?
a User ID (uid).
Every process that runs on the system runs a …?
given uid.
Every file in the file system is owned by a …?
uid
The /etc/passwd file maps uids to…?
user accounts.
User accounts map uids to a…?
username, password, Group Id(s), a home directory, and a login shell.
Passwords are changed with…?
passwd command.
Passwords now store in…?
/etc/shadow
safer to do this, only user root can view file, change password using passwd
Three types of users…?
Normal, root and system.
Normal users…?
- Real people
- Login shell is /bin/bash
- Home directory inside /home
- UID over 500
The root User…?
- UID 0
- Free rein on system: she may modify or remove any file; she may run any command; she may kill any process.
System users…?
- Components of system, not real people
- UID in range 1 -499
- Example : Processes that handle email often run as the username mail
Fundamentally, a group is just…?
an integer group id (gid)
Every process that runs on the system runs…?
under a collection of groups (gids)
The /etc/group file maps gids to…?
group names and group memberships
Every file in the file system is owned by …?
a single gid
Users have a single primary group defined in…?
the /etc/passwd file.
Users may be members of multiple secondary groups, defined in the…?
/etc/groups file.
Every file must have a group owner, there must be a…?
default group associated with each user.
(This default group becomes the group owner of newly created files. This group is known as a user’s primary group. A user’s primary group is defined in the fourth field of a user’s /etc/passwd entry.)
In addition to a primary group, users may optionally belong to…?
other groups as well.
These groups are termed secondary groups, and are defined (coincidentally) in the fourth field of the /etc/group file.
Use usermod and groupmod commands to…?
modify group membership.
The id command displays..?
user and group information.
The whoami command reports…?
the current username
The who, users, and w commands…?
report users with active sessions.
The finger command reports when users were last…?
logged onto the system, and other user information. (A .plain file can be placed in the user’s home directory with more information)
The su command allows a user to…?
switch user id
The su command is usually called with a ..?
hyphen, such as su -, to specify that the user should effectively log in as the new user.
The newgrp command, also called sg, allows a user to…?
switch primary group id.
