In linux, php files cannot be executed after they are replaced by the same file.

In linux, php files cannot be replaced by the same file, but php runs normally. I recently made another php Project. I had a php file on the unit Computer. suppose it was 1.php. I went home and wrote 1.php for one night. When I arrived at the company the next day, I took the Unit 1. php overwrites... Result 1. when php is executed, a blank page is displayed in the browser. I thought it was a problem with the code and overwrite the previous one. php files cannot be executed after they are replaced by the same file in linux.
In a personal LAMP environment, php runs normally.
I recently made another php Project. I had a php file on the unit Computer. suppose it was 1.php. I went home and wrote 1.php for one night. When I arrived at the company the next day, I took the Unit 1. php overwrites... Result 1. when php is executed, a blank page is displayed in the browser. I thought it was a problem with the code and overwrite the previous one. the PHP file was obtained from the USB flash drive and overwritten again. The result is still a blank page...
The code can still run before, no problem. in this way, after two changes, even files that can run previously cannot run. Please help us to see why.

------ Solution --------------------
Ls-al

Root File permission problem. Modify file permission 777