Troubleshooting Tips and Tools

This section provides an overview of some of the most common troubleshooting packages used in Debian. Since one of the biggest parts of an administrator's job is knowing the right tool to use for the job, you may find yourself making your own list of "essential packages" for easy reference.

When Moving From Fedora or Red Hat

Earlier in this appendix, I described the most confusing aspects of Debian, at least for those readers who are moving from Fedora or Red Hat. Here's a refresher:

Use dpkg -L to find files-especially configuration files. Some will be in different places on Debian when compared to Fedora or Red Hat.
/usr/share/doc/packagename/README.Debian (sometimes with an added .gz extension) should be the first thing you check when you run into a problem with a given package.
Always install packages via apt-get. Don't download a random package file from the Web; it will likely break your system badly.
When in doubt, ask somebody who is more familiar with the system than yourself. The "Getting Help" section of this appendix will give you a good walkthrough of, well, getting help. Debian is not only a software distribution, it's also a rich community. Don't shun the community around Debian, as it's one of the most powerful tools available to you.

Troubleshooting Tools

Aside from the simple pointers above, you'll mainly be working with the same software, diagnosing the same problems, and using the same tools as with Fedora or Red Hat. In my experience, the hardest part of any transition is just learning which packages provide which troubleshooting facilities (remember that with Debian, all you need to know is a package's name). So the following tables offer lists of package names with descriptions and tips on further documentation, just to get you started on your transition. Table C-2 covers file system tools; Table C-3 lists network tools; Table C-4 addressed system integrity tools; and Table C-5 offers debugging tools. Unless otherwise specified, full man pages for all the commands are included in the package.

Table C-2: File System Tools
*Package Name*	*Relevant Commands*	*Description*
e2fsprogs	fsck.ext2, fsck.ext3, mkfs.ext2, mkfs.ext3, resize2fs, tune2fs	Standard utilities for working with ext2 and ext3 filesystems. Of particular note is the resize2fs utility, which allows you to resize an unmounted ext2 or ext3 filesystem.
xfsprogs	mkfs.xfs, fsck.xfs, xfs_repair, xfs_growfs	These are the standard utilities for working with an XFS filesystem. xfs_growfs allows you to expand the size of an XFS filesystem while it's in-use (shrinking is not possible at all). xfs_repair can only be used on an unmounted XFS filesystem.
xfsdump	xfs_fsr	Among other commands, this package includes xfs_fsr- the defragmenter for the XFS filesystem.
reiserfsprogs	mkreiserfs, resize_reiserfs	The reiserfsprogs package includes the standard utilities for working with ReiserFS filesystems-including mkreiserfs (to create such filesystems), and resize_reiserfs (to resize such filesystems).
util-linux	fdisk, cfdisk	fdisk is the traditional filesystem partitioning utility, while cfdisk is a full-screen version which provides for a more pleasant experience.
parted	parted	parted is a newer partitioning utility, and is quite good. It's also capable of resizing many filesystems and partitions. Basic manual pages are provided in the parted package, while full documentation is contained in the parted-doc package.

Table C-3: Network Tools
*Package Name*	*Relevant Commands*	*Description*
iputils-tracepath	tracepath, tracepath6	iputils-tracepath contains modern versions of the venerable traceroute commands. They allow you to view the route any of your Internet packets take on the way to their destination. tracepath6 is IPv6-compatible.
iputils-ping	ping, ping6	Modern versions of the ping command. ping6 includes IPv6 support.
tcptraceroute	tcptraceroute	Similar to tracepath, tcptraceroute allows you to view the route your Internet packets take on the way to their destination. Unlike tracepath, tcptraceroute uses TCP, which allows it to circumvent misconfigured routers.
mtr-tiny	mtr	mtr is an excellent tool for diagnosing connectivity problems at a distance. It is similar to tracepath and traceroute in that it examines each step on a packet's journey, but it's different in that it collects a great deal of statistics and presents them in an organized manner.
monit	monit	monit is a "hearbeat" system. It allows you to monitor your computers and the services running on them in an automated manner. It allows for numerous reporting methods, including pages and e-mail. Documentation for monit is contained in /usr/share/doc/monit/.
netcat, netcat6	nc, nc6	netcat is a versatile tool for network analysis, whose full capabilities can't even be touched here. It's often referred to as "the Swiss Army knife of networking."
ssh	ssh, sshd	The Debian ssh package contains both the OpenSSH client and server. OpenSSH is a secure remote-login protocol that allows for unattended non-interactive logins.
telnet-ssl	telnet	While telnet's usage as a remote login protocol has been diminished in recent years (namely falling due to the convenience of SSH), it's still useful to talk to a network server "in the raw."
dnsutils	dig, nslookup	dnsutils contains dig and nslookup, two stalwart utilities used commonly in diagnosing Domain Name System problems.
openssl	openssl	The openssl package provides a command-line interface to the OpenSSL libraries, which export a large number of cryptographic-related functions.

Table C-4: System Integrity Tools
*Package Name*	*Relevant Commands*	*Description*
aide	aide	AIDE stands for "advanced intrusion detection environment." It keeps track of any changes to files on your system, and will notify you if something has changed when it shouldn't have. It can be difficult to set up and maintain, but the results are quite worth it. Man pages, as well as documentation in /usr/share/doc/aide/.
chkrootkit	chkrootkit	chkrootkit performs some rudimentary tests to check to see if a root kit has been installed on your Debian installation. A root kit is used by malicious crackers to maintain control over an installation they have cracked into.
checksecurity	checksecurity	checksecurity runs automatically each day and will notify you of any changes in setuidor setgid applications. setuid and setgid applications are those which always run with elevated user privileges, regardless of the user who actually runs them.
debsums	debsums	Many Debian packages include cryptographic "hashes" of files that allow one to identify whether a file has been changed since it was installed. debsums is a utility to ensure that no files have been changed. Be warned, though-if an intruder is able to change a file that came from a package, they're also able to change the database of cryptographic hashes. debsums can be thought of as an easy-to-use version of AIDE. (Note: this package is Debian-specific, unlike the others listed in these tables.)
tar	tar	tar is a venerable backup utility, which archives multiple files into a single, optionally compressed file. It can be difficult to use, but its archives are usable on pretty much any modern platform (and several obsolete platforms).
rsync	rsync	rsync is a file-transfer application which allows you to transfer sets of files between two machines. Even more impressive, however, is its ability to keep those two repositories synchronized-it implements a very efficient transfer algorithm which only transfers those parts of the files which have changed.
amanda-client, amanda-server	Too many to list.	Amanda is a popular client/server backup solution that works over a network. Documentation is available via man pages, /usr/share/doc/amanda-client/, and /usr/share/doc/amanda-server/.
duplicity	duplicity	duplicity is a flexible and secure backup/archiving solution. It supports encryption and incremental backups. It uses the same partial-change algorithm as rsync, meaning incremental backups are quite small in size.

Table C-5: Debugging Tools
*Package Name*	*Relevant Commands*	*Description*
strace	strace	strace allows you to monitor the internal workings of an application. This is particularly useful when the application fails to function but doesn't provide a helpful error message.
Itrace	Itrace	Itrace is similar to strace, but instead of intercepting system calls it intercepts library calls.
gdb	gdb	gdb is the GNU Debugger. It's a very complex debugger used to closely analyze, interactively, the inner workings of an application. It's primarily useful to developers, as knowledge of the application's source code is required, gdb documentation is in texinfo format, contained in the package. To view it, install the info package and then run info gdb.
ddd	ddd	ddd stands for Data Display Debugger. It's a graphical front-end to gdb. ddd documentation is in texinfo format, contained in the package. To view it, install the info package and then run info ddd.