UNIX for Dummies Questions & Answers

is there any reason why a user would want to create an empty file in Unix?

Empty files are sometimes used as flag files for other processes - though IPC could always be employed.

Other programs use them to mark certain conditions - a good example would be Big Brother's acknowledgment files. It has also been employed in the past for high availability packages to mark conditions know to the SA that shouldn't force a switch.

What prompts the question?

thanks for the reply!!

I had been reading some material on unix and ran across the topic of creating empty files

Sometimes makefiles also create empty files just to remember the most recent time when the last make process occurred.

Also, when you use the vipw command a lock file is created... to prevent other modification of the passwd file while you are using it.



from the man page for vipw...


An /etc/ptmp file not removed when a system crashes prevents further
editing of the /etc/passwd file using vipw after the system is
rebooted. /etc/ptmp is the standard lock used by all commands which
knowingly modify /etc/passwd.

Generally the zero size files are used as flags as said by keith, and again keith says that IPC are also used.

It is always better to use the semaphores in such case rather than the zero size files, as the file IO can raise performance issue. but again, if one uses the semaphores, I beleive the semaphores are deleted if the system is rebooted!! in that case one might loose these flags !!!