chmod

Who can read, write and run a file: chmod in letters (u+x) and numbers (755), with a calculator.

>_ Try it: a simulated Linux, right herenothing runs on your computer

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Examples

chmod +x deploy.sh make a script runnable
./deploy.sh run it
chmod 644 deploy.sh owner writes, everyone reads
chmod u=rwx,go=rx deploy.sh the same as 755, in letters
chmod 600 deploy.sh private: only the owner
chmod -R 755 site a whole folder at once

How it works

Every file has three sets of permissions: the owner (u), the group (g) and everyone else (o). Each set can read (r), write (w) and execute (x). ls -l shows them as rwxr-xr-x.

Numbers are a shortcut: r = 4, w = 2, x = 1. Add them up for each set: rwx = 7, r-x = 5, so 755. And 644 is rw- r-- r--: the owner writes, everyone reads.

Syntax

chmod [OPTION] MODE FILE...

Options

Option	What it does
`u g o a`	who: user (owner), group, others, all
`+ - =`	add, remove, or set exactly
`r w x`	read, write, execute
`755`	the same in numbers (owner, group, others)
`-R`	a folder and everything inside it

Good to know

chmod 777 gives everyone everything: almost never the fix you want.
A script needs x to run with ./; a folder needs x to be entered with cd.