Solution to the problem of PHP mkdir() without write permission

When using mkdir to create a folder, I found that this function has two parameters. The second parameter specifies permissions for the newly created folder.

But if you use mkdir('file address', 0777); directly, you will find that the permissions of the new folder are not 777, but usually 022.

Because when mkdir sets permissions for a folder, it performs a bitwise AND with the umask (user default permission attribute) value of the user currently logged in to the operating system, and the resulting value is the final permission value.

umask What is it?

How do we get the default permissions for files we create? How to change this default permission?

When we log in to the system and create a file, there is always a default permission. So where does this permission come from? This is what umask does.

umask sets the default permissions for files created by users. It has the opposite effect to chmod. umask sets the permission "complement code", while chmod sets the file permission code. Generally, the umask value is set in /etc/profile, $HOME/.bash_profile or $HOME/.profile.

How to calculate umask value? The

umask command allows you to set the default mode when creating files. There is a corresponding number in the umask value for each type of user (file owner, user in the same group, other users). For files, the maximum value of this number is 6. The system does not allow you to give execution permission to a text file when you create it. You must use the chmod command to increase this permission after creation. Directories allow setting execution permissions, so for directories, the maximum number in umask can be up to 7.

The general form of this command is: umask nnn, where nnn can be 000 - 777.

We just need to remember that umask "takes away" the corresponding bit from the permissions.

For example: if the umask value is 022, the default directory permission is 755 and the default file permission is 644.
So, if the user umask is 022 (usually this is the default), that is: 000 010 010 is equal to 777 specified by mkdir, that is: 111 111 111. After the "AND", the real permission obtained is: 022.

If you want to maximize the permissions of the new folder, there are two ways to achieve it: (of course, under the condition that the current user can grant the highest permissions)

1. Modify the user umask, PHP provides the umask function:

$oldumask=umask(0); 
mkdir('test',0777); 
umask($oldumask);

This method seems to work once and for all. Specify the umask value in the opening file of the script, and then directly use mkdir to control permissions. It should be noted that when using the umask function on a multi-threaded server, multiple threads will share a umask, so May cause confusion.

2. Use the chmod function, which is also the most commonly used method:

mkdir('文件地址', 0777); 
chmod('文件地址', 0777);

Finally, it should be noted that the permission value is best expressed in octal, that is, starting with "0", and be sure not to add quotation marks.

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