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unix file system V filename limit

 
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Old 03-16-2008
The filenames are stored in the directory. A directory is a table with a name and an inode number. The directory called "etc" in the "/" filesystem might have an entry like (passwd,3115) and this means that the file called "passwd" is inode 3115, so we can read inode 31115 to get /etc/passwd. The directory does indeed consume space. That's why I said that "space allocated to filenames is not available for file data". If you create a directory and put 10,000 files in it, you will have a large directory and that directory does indeed consume space that otherwise could have been used for file data.

With the original unix file system, directory enties were fixed in size. 14 bytes is all that was allocated to names. This made changing your mind later very hard, but it could have been just as easily designed with a different fixed size. These days just about everyone has variable sized directory entries and that include HP-US UFS which is willing to enforce that 14 character limit.
 
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LEARN ABOUT BSD

savecore

SAVECORE(8)						      System Manager's Manual						       SAVECORE(8)

NAME

       savecore - save a core dump of the operating system

SYNOPSIS

       savecore dirname [ system ]

DESCRIPTION

       Savecore  is  meant to be called at the end of the /etc/rc file.  Its function is to save the core dump of the system (if one was made) and
       to write a reboot message in the shutdown log.

       It saves the core image in the file dirname/core.n and its corresponding namelist in dirname/unix.n.  The second argument is  the  namelist
       for the system which made the core image; the current system is always assumed to be /unix.  The trailing ".n" in the pathnames is replaced
       by a number which grows every time savecore is run in that directory.

       Before savecore writes out a core image, it reads a number from the file dirname/minfree.  If there are fewer free blocks on the file  sys-
       tem  which contains dirname than the number obtained from the minfree file, the core dump is not done.  If the minfree file does not exist,
       savecore always writes out the core file (assuming that a core dump was taken).

       Savecore also writes a reboot message in the shut down log.  If the system crashed as a result of  a  panic,  savecore  records	the  panic
       string in the shut down log too.

       If  savecore detects that the system time is wrong because of a crash (the time in the core image is after the current time), it will reset
       the system time to its best estimate of the time, which is the time in the core image plus the elapsed time since the reboot.  It announces
       the time that it set when this occurs.

FILES

       /usr/adm/shutdownlogshutdown log
       /unix		   current UNIX

BUGS

       The method used to determine whether a dump is present, and to prevent the same core image from being saved multiple times, is not elegant.
       This information should be passed to init by the system; however, this is difficult because the system may have to  be  rebooted  a  second
       time if the root filesystem is patched.

3rd Berkeley Distribution													       SAVECORE(8)