Note: This is Part 2 of 2. Click here to start at the very beginning.

Picking up where we left off at the end of yesterday's post:

Devices, Linux Filesystems, Filesystem Hierarchy Standard

The top ten items to know as you study for this domain are:

1) File and directory permissions can be changed with the chmod command (which accepts numeric and symbolic values).

2) The owner of a group can be changed with the chown command whereas the chgrp command allows changing he group associated with a file.

3) The du command can show how much of a disk is used.

4) The df command shows how much of a disk is free.

5) The main tool for troubleshooting disk issues is fsck which can check filesystem structure, including inodes.

6) To mount filesystems, use the mount command and to unmount them use umount. To have mounting occur automatically at startup, add the entries to /etc/fstab.

7) Quotas can restrict the amount of space users or groups can use on the disk. Quotas are initialized with the quota command and they are toggled on and off with quotaon and quotaoff. They can be changed with edquota and reports can be generated with repquota.

8) When files are first created, the default permissions are equal to 666 minus any umask values. The default permissions for directories is equal to 777 minus any umask values.

9) The mke2fs utility can be used to make the filesystem.

10) Linux supports numerous filesystems including ext2, ext3, ext4, and reiserfs.

Shells, Scripting and Data Management

The top ten items to know as you study for this domain are:

1) Logic can be added to scripts by testing conditions with test or [. Commands can execute using if-then-fi deviations or through looping (while, until, or for). You can leave a script with the exit command or leave a loop with break.

2) Variables can be given at the command line and referenced as $1, $2, and so on, or entered into the executing file with the read command.

3) The alias command can be used to create an alias for a command to operate by another name (for example, being able to type dir and have ls -l performed).

4) Environmental variables can be viewed with the env command.

5) Variables can be added to the environment using the set command and export; they are removed using unset.

6) The /etc/profile configuration file is executed whenever a user logs in.

7) For those using the bash shell, the shell first looks for .bash_profile and if it does not file it, it will look for .bash_login.

8) When the bash user logs out, the shell will look for .bash_logout and execute any commands found there.

9) While other configuration files run only when the user logs in or out, the .bashrc file can execute each time a shell is run.

10) Shell scripts mush have executable permissions to run, or be called by a shell (for example: sh script). The normal exit status of any script or application is 0 and anything else signifies a non-normal exit.

User Interfaces and Desktops

The top ten items to know as you study for this domain are:

1) The emacspeak speech interface is one of the most popular speech interfaces available for Linux.

2) The xdpyinfo utility can be used to view information about an X server.  It can be used with the "all" extension name to see information about all the extensions supported by the server.

3) Window information for X can be viewed with the xwininfo utility. Using the -all parameter shows all the possible information.

4) The server access control program for X is xhost. This is used to connect to a host across the network and work within the graphical interface.

5) The X display manager (xdm) is the default display manager included with the X Window System.

6) The /etc/x11/xorg.conf file is the X configuration file used for initial setup.

7) Several assistive technology projects have been developed for both KDE (the KDE Accessibility Project) and GNOME (the GNOME Accessibility Projects).

8) Orca is a screen reader from the GNOME project intended to help individuals who  are blind or impaired. Orca will work with Firefox, Thunderbird, OpenOffice.org/LibreOffice and other applications.

9) The GNOME onscreen keyboard reader (GOK) is another assistive technology. It works with XML files and can dynamically create keyboards to adapt to a user's needs.

10) Slow keys can be configured for a keyboard preference to only accept input if a key is held and this prevents accidental presses from counting as input. Bounce keys can be configured to ignore fast duplicate key presses and sticky keys can be used to simulate simultaneous key presses.

Administrative Tasks

The top ten items to know as you study for this domain are:

1) Users can be added by manually editing the configuration files or by using the useradd command (and they can be removed with userdel).

2) The groupadd utility can be used to create groups and groupdel can be used to remove groups. Groups can be modified with groupmod and users can change between groups with the newgrp command.

3) To schedule a job to run in unattended mode one time only, you can use the at command.

4) Scheduled jobs can be viewed with the atq command and deleted prior to execution with atrm.

5) Restrictions can be placed on who can use the at service (atd) by creating an at.allow file and only placing valid usernames beneath it.

6) You can create an at.deny file — instead of at.allow — and place in it the names of users who cannot use that at service (meaning that everyone not listed in there can still use it).

7) If you need to schedule an unattended job to run at any sort of regular interval, you can create a crontab (cron table) entry for it.

8) Crontab files are read by the cron daemon, which looks every minute to see if any jobs need to run.

9) Restrictions can be placed on who can use cron by creating a cron.allow or a cron.deny file.

10) There are six fields to each entry in the cron tables: the minute the job is to run (0 to 59), the hour the job is to run (0 to 23), the day of the month (1 to 31), the month of the year (1 to 12), the day of the week (0 to 6), and the path to the executable that is to run.

Essential System Services

The top ten items to know as you study for this domain are:

1) The Network Time Protocol daemon (ntpd) maintains the time on all servers using NTP.

2) The hwclock command can be used to display the data and time of a system's hardware clock (also known as the real time clock).

3) The timezone is configured in the /etc/timezone file. Local time is likewise configured in /etc/localtime.

4) The sendmail service is a general purpose SMTP program used for sending email between servers.

5) The mailq command shows a list of messages in the mail queue and works sendmail.

6) The newaliases command builds a database for the mail aliases file.

7) Mail can be forwarded from one email address to another using a .forward file.

8) Line printers are rarely used anymore, but the support for them remains. The primary utilities associated with them were/are lpr (to submit a print job), lpq (to see the print queue), and lprm (to remove queued print jobs).

9) The Common Unix Printing System (CUPS) is the most common printing interface used on Linux today. It provides support for the line printer daemon as well as Server Message Block (SMB).

10) The kernel logging daemon (klogd) logs Linux kernel messages.

Networking Fundamentals

The top ten items to know as you study for this domain are:

1) IPv4 uses 32-bit addresses divided into four octets. The first octet identifies the class of address (A, B, C). The address can be public or private.

2) The ifconfig utility can be used to see the current IP configuration of the network cards.

3) The ping utility is an all purpose tool for testing connectivity. It will send echo messages to a specified host to see if it can be reached. It can be used with the loopback address (127.0.0.1) to test internal configuration.

4) Instead of using ping, one can use traceroute to see the route taken to reach a particular host.

5) The route utility will display the routing table and allow you to configure it.

6) The netstat utility will show the current status of ports — those that open, listening, etc.

7) The name of the network host is configured in /etc/hostname and can be viewed with the hostname command.

8) You can remotely log into to another host with telnet, but it is highly recommended that this utility no longer be used due to very weak security.

9) Ftp servers can be used to transfer files from one host to another.

10) DNS is used for resolving names to addresses. Utilities that can be used in conjunction with it include dig (for DNS lookup).

Security

The top ten items to know as you study for this domain are:

1) Adding 1000 to standard permissions turns on the "sticky bit", whereas 2000 turns on the SGID permission and 4000 turns on the SUID permission.

2) Links are created with the ln command. A "hard" link is nothing more than an alias to a file (sharing the same inode). A symbolic link is created with ln -s and is an actual file with its own inode. The symbolic link contains a pointer to the original file and can span across filesystems (while the hard link cannot).

3) Passwords are changed with the passwd command. While older systems stored passwords in /etc/passwd, they are now in /etc/shadow where they are more secure.

4) To see who logged on most recently and may currently still be on, you can use the last command.

5) The su command allows you to become another user (returning with exit). If no other username is specified, then the root user is implied, hence the su for superuser.

6) To run a command as another user (usually root) rather than become them, sudo should be used instead of su.

7) The who command will show who is logged on while the w command shows information combining who with uptime.

8) You can limit which hosts can remotely connect by using either a hosts.allow file (only those hosts specifically listed can connect) or hosts.deny (only those hosts specifically listed cannot connect).

9) The ulimit utility can show the number of open file limit in Linux. You can also change the value using this same command.

10) The usermod command changes attributes for a user and modifies their account.

Conclusion

There have been some updates and changes to the Linux+ certification exams recently and they merit looking into if you have not earned this certification already.

Note: This is Part 2 of 2. Click here to start at the very beginning.