a semaphor is nothing but a term used in unix for a variable which acts as a counter.for instance there may be times when two processes try to ACCESS the same file simultaneously.in this EVENT we must control the access of the when the other process is accessing this is done by ASSIGNING value to a semaphore.the value of the semaphore is initialized by the 1ST process when the file is in access by it.when the 2nd process try to access the file it checks the value of the semaphore and if it finds the value as initialized it does not access the file.

a semaphor is nothing but a term used in unix for a variable which acts as a counter.for instance there may be times when two processes try to access the same file simultaneously.in this event we must control the access of the when the other process is accessing this is done by assigning value to a semaphore.the value of the semaphore is initialized by the 1st process when the file is in access by it.when the 2nd process try to access the file it checks the value of the semaphore and if it finds the value as initialized it does not access the file.