Java™ Application Development on Linux - Dator

172Chapter 6The IBM Developer Kit for Linux, Java 2 Technology EditionExample 6.1 Attempt to hardlink between mounts$ ln example /boot/sampleln: creating hard link `/boot/sample' to `example': Invalid cross-device link$Example 6.2 Symlinking /etc/passwd$ ls -latotal 8drwxrwxr-x 2 mschwarz mschwarz 4096 Jul 8 15:30 .drwx------ 50 mschwarz mschwarz 4096 Jul 8 15:29 ..$ ln -sf /etc/passwd passwd$ ls -latotal 8drwxrwxr-x 2 mschwarz mschwarz 4096 Jul 8 15:31 .drwx------ 50 mschwarz mschwarz 4096 Jul 8 15:29 ..lrwxrwxrwx 1 mschwarz mschwarz 11 Jul 8 15:31 passwd -> /etc/passwd$ cat passwdroot:x:0:0:root:/root:/bin/bashbin:x:1:1:bin:/bin:/sbin/nologindaemon:x:2:2:daemon:/sbin:/sbin/nologin...etc.What we did here works just like a hard link, but note the attributeson the file: The l indicates a symbolic link, and the permissions areread/write/execute for user, group, and other (or for “world” for short). However,these permissions apply to the link, not to the file. Just as with hard links,there is only one set of permissions on the file, and these are on the file that ispointed to, not on the pointer.One interesting difference between symlinks and hard links is that symlinksdo not increment the link count on a file. If we remove /etc/password(a very bad idea, by the way), the symlink would be unaffected, but an attemptto open or read the symlink would not work, because it points at nothing thatexists. This is called a dangling symlink.Symlinks may refer to symlinks, and thus you need to be cautious to avoidcircular symlink chains. All the shells we have used on Linux report circularsymlinks as “too many levels of symbolic links,” which sounds like a processexceeding its stack limits but handling it gracefully.