Advanced Programming in the UNIX® Environment

ptg10805159

Section 4.19 File Times 125

Thelscommand displays or sorts only on one of the three time values. By default,

when invoked with either the-lor the-toption, it uses the modification time of a file.

The-uoption causes thelscommand to use the access time, and the-coption causes

it to use the changed-status time.

Figure4.20 summarizes the effects of the various functions that we’ve described on

these three times. Recall from Section 4.14 that a directory is simply a file containing

directory entries: filenames and associated i-node numbers. Adding, deleting, or

modifying these directory entries can affect the three times associated with that

directory.This is why Figure4.20 contains one column for the three times associated

with the file or directory and another column for the three times associated with the

parent directory of the referenced file or directory.For example, creating a new file

affects the directory that contains the new file, and it affects the i-node for the new file.

Reading or writing a file, however,affects only the i-node of the file and has no effect on

the directory.

Parent directory

Function Referenced file of referenced file Section Note

or directory or directory

am c am c

chmod,fchmod •4.9

chown,fchown •4.11

creat ••• •• 3.4 O_CREATnew file

creat •• 3.4 O_TRUNCexisting file

exec •8.10

lchown •4.11

link •••4.15 parent of second argument

mkdir ••• •• 4.21

mkfifo ••• ••15.5

open ••• •• 3.3 O_CREATnew file

open •• 3.3 O_TRUNCexisting file

pipe ••• 15.2

read •3.7

remove •••4.15 remove file =unlink

remove •• 4.15 remove directory =rmdir

rename •••4.16 for both arguments

rmdir •• 4.21

truncate,ftruncate •• 4.13

unlink •••4.15

utimes,utimensat,futimens ••• 4.20

write •• 3.8

Figure 4.20Effect of various functions on the access, modification, and changed-status times

(The mkdir and rmdir functions arecovered in Section 4.21. The utimes,

utimensat,andfutimensfunctions arecovered in the next section. The sevenexec

functions aredescribed in Section 8.10. We describe themkfifoandpipefunctions in

Chapter 15.)