Top Ten Mac OS X Tips for Unix Geeks
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5. Different Kinds of Hidden Files

As with other Unix flavors, you can make a file invisible by prefixing its name with a ., as in /.vol. This has the effect of making it invisible in the Finder, as well as when you issue an ls without the -a option.

Mac OS X also uses a file in the root directory (.hidden) to maintain a list of files that should be hidden from the Finder.

Also, HFS+ (the filesystem used by Mac OS) files and directories can have a hidden attribute set using the SetFile command, as in SetFile -a V SomeFile. (The SetFile command is available in /Developer/Tools after you install the Mac OS X Developer Tools package described in the sidebar.) This setting won't take effect until you relaunch the Finder. You can log out and log in again or use the Force Quit option from the Apple menu. You can turn off the invisible bit with SetFile -a v SomeFile. See the manpage for SetFile for more details. (Note that invisible files are only invisible from the Finder; you can still see them with ls.)

6. Aliases and Links

There are two ways to create links to files. The first is to select the file in the Finder, and drag it to a new location while holding down the Option and Command keys (or select Make Alias from the File menu). This creates a Mac OS alias that Cocoa, Carbon, and Classic applications can follow. However, Unix applications will ignore those links, seeing them as zero-byte files.

You can also create a link with ln or ln -s. If you use this kind of link, Unix, Cocoa, Carbon, and Classic applications will happily follow it.

7. X11

Mac OS X does not come with the X Window System. For native applications, it uses an advanced graphics system called Aqua. But if you want to run X11 applications, you're in luck: Apple has its own X11 implementation with nice Aqua integration, and there is an installer for it on your Mac OS X installation CD-ROM or DVD. If it wasn't installed by default, run the Optional Installs package on your install disc. You'll be able to run X11 applications side-by-side with Mac OS X applications, and they'll look great.

8. Fink

Are there some Unix or Linux applications that you're missing? Check out the Fink project, which modifies open source applications so they'll compile and run on Mac OS X. Fink already includes an impressive array of applications, and more are on the way.

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9. /etc is Not Always in Charge

If you've come to Mac OS X from another Unix, you may expect that you can add users and groups to the /etc/passwd and /etc/group files. By default, Mac OS X only uses these file in single-user mode. If you want to add a user or group, it will need to go into the Directory Services database, a repository of local directory information. For more information, see this ADC article,Open Directory and the dscl Tool.

10. Shutdown Doesn't Really

For a long time, Mac OS X couldn't execute custom actions at shutdown. The SystemStarter framework (which predates launchd) can perform custom shutdown actions when the system is shutting down. For more information, see "Start Me Up: Writing and Understanding OS X StartupItems" (the ADC launchd article mentions that services that need an explicit shutdown procedure will need the old SystemStarter framework).

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In September 2002, O'Reilly Media released Mac OS X for Unix Geeks.

Brian Jepson is an O'Reilly editor, programmer, and co-author of Mac OS X Panther for Unix Geeks and Learning Unix for Mac OS X Panther. He's also a volunteer system administrator and all-around geek for AS220, a non-profit arts center in Providence, Rhode Island. AS220 gives Rhode Island artists uncensored and unjuried forums for their work. These forums include galleries, performance space, and publications. Brian sees to it that technology, especially free software, supports that mission. You can follow Brian's blog here.

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