Managing users in Linux. Passwords are kept in:

/etc/passwd

/etc/shadow.

Start a second X session:

$ startx -- :1 vt8

Restrictions on the root account:

(On most) root can logon from the console only.

To take over an account:

# su george

Execute a command as the root account:

$ sudo

Who may use sudo:

/etc/sudoers

It is possible to set a program to always run as if ran by the root account. No matter who runs the program:

SUID root files: a special bit (attribute) is set.

User names:

Usernames cannot start with a number.

Usernames may be 32 characters in length.

Usernames are case sensitive.

General rule:

Avoid using punctuation.

This command WILL remove all of your system! WARNING as root account:

# rm –r /

This command will remove the olddir.

# rm –r /home/george/olddir

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useradd

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passwd

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·  Windows98 SE

usermod

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userdel

# find / -uid 529

grpadd

gpasswd

# find / -gid 503

Directory and file Access Components

The directory permissions above:

drwx r-x r-x

 ----- ---- ----

Similar file permissions:

-rwxrw---

Changing file ownership permissions

chown changes a file’s owner and optionally, its group:

                       Where               what

# chown [options] [.newgroup] filename

# chown sally.projects2 report.tex

Used with chown, hanges all the files within a directory.

--recursive

# chgrp

Octal value for permissions:

Set user ID (SUID)

rwsr-x--x

Set group ID (SGID)

rwxrwS--x

Indicated by an (s) in the execute section of the (u) user section of super user ID, and in the execute section of the group permissions.

Sticky bit:

When this bit is present on a directory, the directory’s files can only be deleted by their owners, the directory’s owner, or root.

The sticky bit is indicated by a (t) in the world execute bit position.

drwxr-xr-t