Advanced Programming in the UNIX® Environment

ptg10805159

274 Process Control Chapter 8

BSD-derived platforms don’t support theac_stat member, so we define the

HAS_AC_STATconstant on the platforms that do support this member.Basing the

defined symbol on the featureinstead of on the platform makes the code read better and

allows us to modify the program simply by adding the new definition to our

compilation command. The alternative would be to use

#if !defined(BSD) && !defined(MACOS)

which becomes unwieldy as we port our application to additional platforms.

We define similar constants to determine whether the platform supports theACORE

andAXSIGaccounting flags. We can’t use the flag symbols themselves, because on

Linux, they aredefined asenumvalues, which we can’t use in a#ifdefexpression.

To perform our test, we do the following:

1. Become superuser and enable accounting, with theacctoncommand. Note
   that when this command terminates, accounting should be on; therefore, the
   first record in the accounting file should be from this command.


2. Exit the superuser shell and run the program in Figure8.28. This should
   append six records to the accounting file: one for the superuser shell, one for the
   test parent, and one for each of the four test children.
   Anew process is not created by theexeclin the second child. Thereisonly a
   single accounting recordfor the second child.


3. Become superuser and turn accounting off. Since accounting is offwhen this
   acctoncommand terminates, it should not appear in the accounting file.


4. Run the program in Figure8.29 to print the selected fields from the accounting
   file.

The output from step 4 follows.We have appended the description of the process in

italics to selected lines, for the discussion later.

accton e =1,chars = 336, stat = 0: S

sh e =1550, chars = 20168, stat = 0: S

dd e =2,chars = 1585, stat = 0: second child

a.out e =202, chars = 0, stat = 0: parent

a.out e =420, chars = 0, stat = 134: F first child

a.out e =600, chars = 0, stat = 9: F fourth child

a.out e =801, chars = 0, stat = 0: F third child

For this system, the elapsed time values aremeasured in units of clock ticks.

Figure2.15 shows that this system generates 100 clock ticks per second. For example,

thesleep(2)in the parent corresponds to the elapsed time of 202 clock ticks. For the

first child, thesleep(4)becomes 420 clock ticks. Note that the amount of time a

process sleeps is not exact. (We’ll return to thesleepfunction in Chapter 10.) Also, the

calls toforkandexittake some amount of time.

Note that theac_statmember is not the true termination status of the process, but

rather corresponds to a portion of the termination status that we discussed in