How chmod octal permissions work
Build each octal digit from read 4, write 2, and execute 1, then add the leading special-bits digit.
Read guideUnderstand Unix mode bits
Octal digits, special bits, files, and directories
Three focused guides explain the 12-bit 0000–7777 model, s/S/t/T display, and why read, write, and execute mean different operations for files and directories.
Setuid, setgid, sticky, and the meaning of s/S/t/T
Decode the leading octal digit and understand how each special bit shares a display position with execute.
Read guideChmod permissions for files versus directories
Understand why read, write, and execute bits describe different operations for regular files and directories.
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