I don't tend to use hard links, but they are useful in that you won't run into the 'broken link' issue. i.e. you can move either file, but the link won't break. You can also remove either file without breaking a link. Soft links are less confusing, though, because it's immediately apparent that one is a link. With hard links, you need to look at the output of ls -i to see what inode the file is stored at.
On Wed, Mar 3, 2010 at 10:36 PM, Blues Renegade <[email protected]>wrote: > > Thanks for the clarification, Daniel! Why use hard links at all? They must > exist for a reason, but I have yet to encounter a need that ONLY a hard link > could fill. In commercial UNIX apps I've installed I've only ever seen soft > links used by the software vendor, never hard links. What am I missing here? > > Thanks again, Daniel! Despite my error on hard links, I do hope DOS-MAN got > something out of all I wrote on soft links, or I wasted my time. > > John > > > Daniel Eggleston wrote: > >> An important point that should be made: a link is always a link, and never >> a copy! A hard link is not a copy. A hard link is a duplicate inode >> pointer, so both are "real" files. i.e.: >> >> $ echo "foo" > fileA >> $ ln fileA fileB >> $ ln -s fileA fileC >> $ cat file B >> foo >> $ echo "bar" > fileA >> $ cat fileB >> bar >> $ cat fileC >> bar >> $ rm fileA >> $ cat fileB >> bar >> $ cat fileC >> *error* >> >> The difference between a hard link and a soft link is, the soft link >> points to a file by name. A hard link points by inode, so after you remove >> the original file, it still exists with the second filename. But they're >> not separate copies, they're the same file! >> >> On Wed, Mar 3, 2010 at 7:32 AM, Blues Renegade >> <[email protected]<mailto: >> [email protected]>> wrote: >> >> >> I think you're making it much harder for yourself by mentally >> cross-referencing everything in Linux back to your DOS/Windows >> knowledge. You'll have a much easier time if you "forget" about >> DOS/Windows and approach Linux like a kid learning about computers >> for the first time. >> >> When I first got into Linux, I decided to go back to where Linux >> came from and picked up some old UNIX books where everything was >> done on the command line, they didn't even have an X-server yet, >> and to this day, most UNIX server admins run a console-system >> only, no GUI! Most would never dream of using a GUI, seeing it as >> a headache; more programs and config files to break and wreak >> havoc on the server's stability. >> >> As for links, they are fairly straightforward. There are 2 kinds: >> hard links and soft links. >> >> A hard link is actually just a copy of a file. Personally, I have >> never used hard links. I use cp -a (-a archives a file with its >> original date/time and preserves ownership and permissions) if I >> want to duplicate files. >> >> A soft link is a shortcut to a file; under the covers it's nothing >> more than a pointer that contains the path to where the file exists. >> >> IMPORTANT! The path it stores is the text you enter when you >> create the link. The ln command does NOT try and validate your >> path. The UNIX/Linux philosophy is that commands are small >> programs with a very specific purpose. If you want/need more >> functionality, then you are expected to combine the commands using >> piping and/or redirection to get the job done. Once you learn >> enough commands and know how to combine them, the light bulb will >> go on and you'll realize the true power of UNIX (in our case, Linux). >> >> CREATING LINKS: >> >> For example, you're in your home directory and you want a quick >> way to 'cd' to a /home/dos-man/programming/c/linux/utilities. >> >> Here's a FLAWED WAY of creating a soft link... I'm showing you a >> pitfall first: >> >> ln -s ./programming/c/linux/utilities/ c-utils >> >> ln = link command >> >> -s = soft link (shortcut, pointer, stored path, however you want >> to remember it) >> >> ./programming/c/linux/utilities = a relative path (relative >> reference) to the directory utilities >> >> The period at the beginning points to the current directory. (Not >> very exact is it?!) >> >> c-utils = the filename of your link (shortcut) i.e. this is what >> you'll use with cd to save typing that long path >> >> You're working away in /home/dos-man/programming/c/dos/ and you >> decide to go work on a linux utility, so you run: >> >> cd c-utils >> >> and surprise, it fails! >> >> What it does is try to cd from your current directory to your >> link's path. The cd command replaces the period in the link with >> your current directory and tries to change to the new "fangled" >> (mangled is more like it) path: >> >> It's as though you entered: >> >> cd /home/dos-man/programming/c/dos/programming/c/linux/utilities/ >> >> No such path exists on your system (and if by chance it does, then >> you're not where you expect to be!!). >> >> **** TIP: When creating softlinks, include the complete path (AKA >> absolute reference). >> >> >> To fix the problem above, rm c-utils to remove the link you created. >> >> Re-create it with the complete path this time (an absolute reference). >> >> ln -s /home/dos-man/programming/c/linux/utilities/ c-utils >> >> **** TIP: It's a good idea to include the trailing slash when >> creating links to directories, so when you look at the link with >> 'ls -l', you'll know it's pointing to a directory. >> >> >> Hope that helps you to start using links right away. >> >> BEST TIP OF ALL: Forget registries, forget Windows, forget DOS, >> and you'll have a much easier time learning Linux!! Start fresh; >> after all, UNIX came first, then MS-DOS borrowed heavily from UNIX >> and ended up as a very watered down proprietary sub-set with some >> subtle (proprietary?). >> >> Many of the commands in UNIX were never replicated in DOS, so they >> will be completely new to you. New concepts and ways of thinking >> to grasp. While DOS had piping and redirection, without a rich >> command set you were still very limited in comparison to UNIX. >> >> John >> >> > -- > You received this message because you are subscribed to the Linux Users > Group. > To post a message, send email to [email protected] > To unsubscribe, send email to [email protected] > For more options, visit our group at > http://groups.google.com/group/linuxusersgroup > -- Daniel -- You received this message because you are subscribed to the Linux Users Group. To post a message, send email to [email protected] To unsubscribe, send email to [email protected] For more options, visit our group at http://groups.google.com/group/linuxusersgroup
