apropos, whatis and makewhatis
This month's column looks at three very useful and related commands, apropos, whatis and makewhatis. To understand why these commands are so valuable, it helps to grasp the underlying philosophy that continues to guide evolving versions of Unix, including Linux. That philosophy remains one of creating small, portable, specialized programs that perform one task well, and that can receive input from, and redirect output to, other programs.
This philosophy has created a proliferation of small, powerful, but extremely limited programs. Just do a directory listing of /usr/bin, and you'll see what I mean. And that's not all of them. You could sit down and run every one of them to see what they do. Or you could begin reading the hundreds of man pages available describing these commands. No matter which method you use to learn the commands, in the end, you'd still probably forget most of them due to the sheer volume. So how do you know which of the hundreds of programs available can do the job for you? Or which of the commands will be best suited to your particular needs? apropos and whatis come to the rescue.
Apropos, as defined by the dictionary, means “apt; relevant; suited to the occasion, though not strictly belonging to the subject under consideration.” These definitions, particularly the last one, are totally apropos. apropos will list programs with a one line synopsis of each program based on a keyword search. whatis is similar, but even more constrained; i.e., the actual command is given as the argument, rather than a keyword, so there is less output.
Before we look at how apropos can help us, we need to ensure that the database apropos uses exists and is up-to-date. Enter makewhatis. This command creates the whatis database files used by both apropos and whatis. They are located in each ../man directory and catalog the manual files in each of the individual cat? and man? subdirectories.
To create the whatis database files, you need to invoke makewhatis as the root user. Non-privileged users normally do not have write permission in the ../man directories to create the whatis database files. A second clue to the nature of makewhatis is its location. makewhatis is usually found in the /usr/sbin subdirectory, indicating its classification as a system administration program. Ordinarily only root's PATH environment variable contains the sbin directories. makewhatis may be invoked by root's crontab file and run on a recurring basis, and you may wish to include it if it isn't already there. But that is beyond the scope of this article. If you can log in only as a non-privileged user, or are sure your whatis database files exist, you may want to skip ahead to the next section. If you begin to see <keyword>: nothing appropriate, you'll need to have your system administrator run makewhatis.
Running makewhatis for the first time will take several minutes, so be patient (go have a cup of coffee). Run by itself, makewhatis will create the whatis database file in /usr/man. To ensure that all the man locations are cataloged, use the -w switch. This will read the file /etc/man.config and use the man paths it specifies. Or you may add paths following the -w switch and they will be used as well. If you are want to know which paths will be cataloged, type man --path, and you will see where /etc/man.config believes your manuals are. If you have other paths, they should be added to your man.config file.
Another makewhatis option is -c. This switch, when used alone, will catalog only the ../man/cat entries listed in man.config. Other cat subdirectories may be added following the -c switch, and they will also be cataloged.
You may, however, want only to update the whatis databases with newly added commands. Use the -u switch to update the database files. This switch reads the time of the whatis database file and adds those manual pages created or updated since.
If you want to know what makewhatis is doing, add the -v switch, and you will see each man directory entered and each command as it is added to the list. Each switch used with makewhatis should be separated by a space and preceded by a hyphen; the switches cannot be combined. makewhatis does have one weakness: if your system does not have sufficient RAM and virtual memory, makewhatis will fail. If you get an error message—and you are running makewhatis as root—add more swap space and try again.
Practical Task Scheduling Deployment
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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- Stunnel Security for Oracle
- The Firebird Project's Firebird Relational Database
- Murat Yener and Onur Dundar's Expert Android Studio (Wrox)
- SUSE LLC's SUSE Manager
- Managing Linux Using Puppet
- My +1 Sword of Productivity
- Non-Linux FOSS: Caffeine!
- Doing for User Space What We Did for Kernel Space
- Google's SwiftShader Released
- SuperTuxKart 0.9.2 Released
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This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide