Ubuntu Unleashed, Second Edition

6. The TERM environment, if it has been set, is preserved.

7. The HOME, PATH, SHELL, TERM, MAIL, and LOGNAME environment variables are set. (If the

-p option is used, all preexisting environmental variables are preserved.)

8. The PATH defaults to /usr/local/bin:/bin:/usr/bin: for normal users and to

/sbin:/bin:/usr/sbin:/usr/bin for root.

9. Normal greeting messages and mail checking are disabled if the file .hushlogin

exists in the users’ home directory; otherwise, those messages display at the end of

the logon process.

10. The user’s command shell is started at this point, presenting the user with a

command prompt. If no shell is specified for the user in

/etc/passwd, /bin/sh is

used by default. (Some UNIX operating systems will just log you back out.) If no

home directory is specified in

/etc/passwd, / is used.

When you log in as a regular user, the files that control your environment are found in

your

/home/username directory. These configuration files are normally hidden from view

because their filename is preceded by a period (as in

.bashrc—these are known as dot

files).

The name of the file indicates which program it is associated with. The files

.bash_

logout, .bash_profile, and .bashrc all determine how the bash shell is used by the user.

(These files can, of course, be preset by the system administrator with the user given only

read access, so the files cannot be changed. Other shells have their own associated files.)

Other files might be present depending on the system and the system administrator. The

point is that the environment of each user can be set globally through the use of files in

/etc/skel and individually by allowing user modification of the files in their /home direc-

tory (or not, depending on the system administration policies).

The system logs all user logins, as well as all uses of

su and sudo commands for the sysad-

min’s review. (The

init, syslogd, and klogd applications create the logs.) Modern secu-

rity-monitoring programs (or simple scripts you create) can scan these files (such as

/var/log/messages) for anomalies and signal possible security violations.

Disk Quotas

On large systems with many users, you need to control the amount of disk space a user

has access to. Disk quotas are designed for this purpose. Quotas, managed per each parti-

tion, can be set for both individual users as well as groups; quotas for the group need not

be as large as the aggregate quotas for the individuals in the groups.

Disk Quotas

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When files are created, both a user and a group own them; ownership of the files is

always part of the metadata about the files. This makes quotas based on both users and

groups easy to manage.

NOTE

Disk quota management is never done on a home system and rarely, if ever, done on a

small office system.

To manage disk quotas, you must have the quota package installed on your system. Quota

management with Ubuntu is not enabled by default and has traditionally been enabled

and configured manually by system administrators. Sysadmins use the family of quota

commands, such as

quotacheck to initialize the quota database files, edquota to set and

edit user quotas,

setquota to configure disk quotas, and quotaon or quotaoff to control

the service. (Other utilities include

warnquota for automatically sending mail to users over

their disk space usage limit.)

Implementing Quotas

To reiterate, quotas might not be enabled by default, even if the quota software package is

installed on your system. When quotas are installed and enabled, you can see which

partitions have either user quotas, group quotas, or both by looking at the fourth field in

the

/etc/fstab file. For example, one line in /etc/fstab shows that quotas are enabled

for the

/home partition:

/dev/hda5 /home ext3 defaults,usrquota,grpquota 1 1

The root of the partition with quotas enabled will have the files quota.user or

quota.group in them (or both files, if both types of quotas are enabled), and the files will

contain the actual quotas. The permissions of these files should be

600 so that users

cannot read or write to them. (Otherwise, users would change them to allow ample space

for their music files and Internet art collections.) To initialize disk quotas, the partitions

must be remounted. This is easily accomplished with the following:

# mount -o ro,remount partition_to_be_remounted mount_point

The underlying console tools (complete with man pages) are

. quotaon, quotaoff—Toggles quotas on a partition

. repquota—A summary status report on users and groups

. quotacheck—Updates the status of quotas (compares new and old tables of disk

usage); it is run after

fsck

. edquota—A basic quota management command

CHAPTER 14 Managing Users

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