Unix: Time access of a File

ctime, atime, and mtime

It is important to distinguish between a file or directory's change time (ctime), access time (atime), and modify time (mtime).

ctime -- In UNIX, it is not possible to tell the actual creation time of a file. The ctime--change time--is the time when changes were made to the file or directory's inode (owner, permissions, etc.). The ctime is also updated when the contents of a file change. It is needed by the dump command to determine if the file needs to be backed up. You can view the ctime with the ls -lc command.

atime -- The atime--access time--is the time when the data of a file was last accessed. Displaying the contents of a file or executing a shell script will update a file's atime, for example. You can view the atime with the ls -lu command.

mtime -- The mtime--modify time--is the time when the actual contents of a file was last modified. This is the time displayed in a long directoring listing (ls -l).

In Linux, the stat command will show these three times.

Examples

$ cat file
file's atime is updated.

$ chmod g+w file
file's ctime is updated.

$ echo "File contents" > file
file's ctime and mtime are updated.

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