Types and meanings of Linux file times

Types and meanings of Linux file times

In the Linux operating system, each file has three different types of timestamps, namely access time (atime) , modification time (mtime) and change time (ctime). These three timestamps record file changes under different operations. Their meanings will be explained in detail below and corresponding code examples will be provided.

1. Access time (atime):
   Access time refers to the last time the file was accessed. Atime is updated when the file is read, run or browsed. atime records the time the file was accessed, but does not affect the content and attributes of the file. Under normal circumstances, atime updates will cause system performance degradation, so it is sometimes turned off.

Sample code:

touch test.txt
ls -l test.txt
# 输出：-rw-r--r-- 1 user user 0 Apr 1 10:00 test.txt
cat test.txt
ls -l test.txt
# 输出：-rw-r--r-- 1 user user 0 Apr 1 10:01 test.txt

2. Modification time (mtime):
   Modification time refers to the last time the file content was modified. mtime is updated when a file is edited, written to or modified. mtime records changes in file content, which may affect the file's attributes. Therefore, mtime is usually used to determine whether a file has been modified.

Sample code:

touch test.txt
ls -l test.txt
# 输出：-rw-r--r-- 1 user user 0 Apr 1 10:00 test.txt
echo "Hello, world" > test.txt
ls -l test.txt
# 输出：-rw-r--r-- 1 user user 13 Apr 1 10:01 test.txt

3. Change time (ctime):
   Change time refers to the time when the file status was last changed. ctime is updated when a file's permissions, owner, or number of links change. At the same time, ctime is also updated when files are created or deleted. Therefore, ctime records changes in file status, not just changes in file content.

Sample code:

touch test.txt
ls -l test.txt
# 输出：-rw-r--r-- 1 user user 0 Apr 1 10:00 test.txt
chmod 777 test.txt
ls -l test.txt
# 输出：-rwxrwxrwx 1 user user 0 Apr 1 10:01 test.txt

Summary:
In Linux systems, file timestamps include access time (atime), modification time (mtime) and change time (ctime) . By understanding the meaning of these three timestamps, we can better understand the changes in files and manage and monitor files as needed. At the same time, in programming development, these timestamps can also be used to implement related functions of file operations.

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