<\/p>\n\n\n\n
When people say:<\/p>\n\n\n\n
\nMax permissions on a file: 666<\/strong><\/p>\n<\/blockquote>\n\n\n\n
they usually mean default maximum permissions when a new regular file is created<\/strong>, not the maximum you can manually set.<\/p>\n\n\n\n
1. Default maximum for new files:
666<\/code><\/h2>\n\n\n\nFor a new regular file<\/strong>, Linux normally starts from:<\/p>\n\n\n\n
666 = rw-rw-rw-\n<\/code><\/pre>\n\n\n\nThat means:<\/p>\n\n\n\n
owner = read + write\ngroup = read + write\nothers = read + write\n<\/code><\/pre>\n\n\n\nNo execute permission by default.<\/p>\n\n\n\n
Why? Because most new files are text files, data files, documents, config files<\/strong>, etc. They should not automatically be executable.<\/p>\n\n\n\n
Example:<\/p>\n\n\n\n
touch file1.txt\nls -l file1.txt\n<\/code><\/pre>\n\n\n\nYou may see something like:<\/p>\n\n\n\n
-rw-r--r-- 1 user user file1.txt\n<\/code><\/pre>\n\n\n\nThe actual permission is affected by the umask<\/strong>.<\/p>\n\n\n\n
\n\n\n\n2. Default maximum for directories:
777<\/code><\/h2>\n\n\n\nFor a new directory<\/strong>, Linux normally starts from:<\/p>\n\n\n\n
777 = rwxrwxrwx\n<\/code><\/pre>\n\n\n\nWhy? Because directories need
x<\/code> permission to be entered or searched.<\/p>\n\n\n\nExample:<\/p>\n\n\n\n
mkdir dir1\nls -ld dir1\n<\/code><\/pre>\n\n\n\nYou may see:<\/p>\n\n\n\n
drwxr-xr-x 2 user user dir1\n<\/code><\/pre>\n\n\n\nAgain, the final permission is affected by the umask<\/strong>.<\/p>\n\n\n\n
\n\n\n\n3. What if I give a file
777<\/code>?<\/h2>\n\n\n\nYou can manually give a file
777<\/code>:<\/p>\n\n\n\nchmod 777 file1.txt\nls -l file1.txt\n<\/code><\/pre>\n\n\n\nOutput:<\/p>\n\n\n\n
-rwxrwxrwx 1 user user file1.txt\n<\/code><\/pre>\n\n\n\nThis means:<\/p>\n\n\n\n
owner = read + write + execute\ngroup = read + write + execute\nothers = read + write + execute\n<\/code><\/pre>\n\n\n\nSo everyone can read, modify, and execute the file<\/strong>.<\/p>\n\n\n\n
\n\n\n\n4. Is
777<\/code> allowed?<\/h2>\n\n\n\nYes, it is allowed.<\/p>\n\n\n\n
But it is usually not safe<\/strong>.<\/p>\n\n\n\n
For a regular file,
777<\/code> means any user can change the file and possibly run it as a program or script.<\/p>\n\n\n\nFor example, this is risky:<\/p>\n\n\n\n
chmod 777 script.sh\n<\/code><\/pre>\n\n\n\nbecause any user may be able to modify the script and then execute it.<\/p>\n\n\n\n
\n\n\n\n5. Better permissions<\/h2>\n\n\n\n
For a normal text\/config\/data file:<\/p>\n\n\n\n
chmod 644 file.txt\n<\/code><\/pre>\n\n\n\nMeaning:<\/p>\n\n\n\n
owner can read\/write\ngroup can read\nothers can read\n<\/code><\/pre>\n\n\n\nFor a private file:<\/p>\n\n\n\n
chmod 600 file.txt\n<\/code><\/pre>\n\n\n\nFor a script that only the owner should run:<\/p>\n\n\n\n
chmod 700 script.sh\n<\/code><\/pre>\n\n\n\nFor a script others can read and execute but not modify:<\/p>\n\n\n\n
chmod 755 script.sh\n<\/code><\/pre>\n\n\n\n
\n\n\n\nSimple summary<\/h2>\n\n\n\n
666 = normal maximum default for new files\n777 = normal maximum default for new directories\n777 on a file is possible, but usually unsafe\n<\/code><\/pre>\n\n\n\nSlide-friendly version:<\/p>\n\n\n\n
\nLinux does not give execute permission to new regular files by default. New files start from a maximum of
666<\/code>, while directories start from777<\/code> because directories need execute permission to be entered. A file can be changed to777<\/code> manually, but this gives everyone read, write, and execute access, which is usually insecure.<\/strong><\/p>\n<\/blockquote>\n\n\n\n<\/p>\n\n\n\n
<\/p>\n\n\n\n
REF: AI Tools\/ChatGPT<\/p>\n","protected":false},"excerpt":{"rendered":"
When people say: Max permissions on a file: 666 they usually mean default maximum permissions when a new regular file is created, not the maximum you can manually set. 1. Default maximum for new files: 666 For a new regular file, Linux normally starts from: That means: No execute permission by default. Why? Because most … <\/p>\n