Java™ Application Development on Linux - Dator

6.2 Use Linux Features to Make Multiple Java SDKs Play Nicely Together171case (we don’t want to muddy the waters with LVM 1 or RAID 2 at thispoint—most Linux distributions do not do LVM or RAID “out-of-the-box”),if you have more than one partition or disk drive, these are “mounted” at differentpoints on the directory tree. For example, Mr. Schwarz’s laptop’s mounttable looks like this:$ mount/dev/hda2 on / type ext3 (rw)none on /proc type proc (rw)usbdevfs on /proc/bus/usb type usbdevfs (rw)/dev/hda1 on /boot type ext3 (rw)none on /dev/pts type devpts (rw,gid=5,mode=620)none on /dev/shm type tmpfs (rw)$We have one large partition mounted at /, or root, and a small partitionmounted at /boot. In all of our hard link examples so far, we have been makinglinks on the root filesystem. Example 6.1 shows what happens when an attemptis made to hardlink between two different mounted devices.This is what we mean when we say a link cannot cross filesystems. 3The other problem is more “touchy-feely.” With a hard link, you can seeby the link count that other links exist, but you don’t know where they are.Symbolic links get you around both of these issues.6.2.1.2 Symbolic Links, or SymlinksIn a sense, symbolic links are much simpler than hard links. A symbolic link isa file that contains the name of another file or directory. Because it is markedas a symbolic link, the system will replace it with the contents of the linked file.Example 6.2 will make this more clear.1. Logical Volume Manager. This is a tool that lets you arbitrarily aggregate disk drives andpartitions into a “logical volume” that may be mounted and unmounted as a unit. Such toolsare commonly used in serious production servers, but are rare on workstations or simple Linuxservers.2. Redundant Array of Inexpensive Disks. Another heavy server feature that allows multipledisk drives to be linked up as if they were a single disk drive and to act as backup to one anothersilently and transparently.3. In a similar vein, there are some networked filesystems that do not support hard links at allbecause the server or host system doesn’t support the concept. Attempts to make links on orto such systems will also fail.