File Permission Systems in Computer

File permissions system: eg drwxr-xr-x this is a 9 or 10 letter string (if 10 letters then the first one will tell either it is file or directory, d means directory and dash(-) for file) rest 9 letters can be divided into 3x3, in which the first three permission are for owner(U), the mid three letters are for group(G) and the last three letters are for public/others(O). There the first letter out each three are read(r), the second write(w) and the third execute(x). If any of these permission isn't give to any user then that place is filled by dash(-) other the letter is present.

# there are two kinds of representation of permission systems: numeric and symbolic. The above was explanation of symbolic.

# the numeric permission representation is from 000 to 777. The first character is for owner(who created the file), the second is for group and the third for public/others. The values of different permission are as: read=4, write=2, execute=1. If some permissions aren't given then its values will be zero. Eg. r_e will have value of 4+0+1=5; we can do this for other users too and compile them in order in a three digit number and that would represent the permission.