https://www.cyberciti.biz/faq/howto-set-readonly-file-permission-in-linux-unix/


Change file attributes on a Linux file system to read-only using the `chattr` command:

```sh
chattr +i /path/to/file.php
chattr +i /var/www/html/

# find everything in /var/www/html and set to read-only #
find /var/www/html -iname "*" -print0 | xargs -I {} -0 chattr +i {}
```

```sh
To remove read-only attribute pass the -i option:
# chattr -i /path/to/file.php
```

FreeBSD, Mac OS X and other BSD unix user need to use the `chflags` command:

```sh
# set read-only
chflags schg /path/to/file.php

# remove read-only
chflags noschg /path/to/file.php
```