I just installed nemo and I am displaying the octal permission field. The permissions are things like 40755 and 100755. I am familiar with the last three digits (755) and I assume those are rwx permissions for owner, group and everyone else. What are the prefix permissions - the 40 and the 100 in my example?
They are the file type. 10 is a fifo, and 40 is a directory. From
Remark/correction: octal permission is given on 7 positions:0000000 lets call them gfedcba.
Position "a" is for "others" and is the sum of the rights : 1 (execute or enter for a directory), 2 (write) and 4 (read). exemple: 7 is 4+2+1; 6 is 4+2 ...
Postion "b" is the same but for "group"
Position "c" is for the "owner"
Position "d" is for the sum of the special carracters: 1 for sticky (only the owner can rename or delete a file if this is set wathever are the other permissions) 2 for forced group (group of a new file will be the dir's group if the owner of the file is allowed to "write" in that dir) 4 for forced owner (owner of a new file will be the dir's owner if the real owner (the creator) of the file have the "write" permission in the dir)
Position "e" to "g" is for the "node" type: (001 is a FIFO) (002 is a carracter device) 004 is a dir 006 is a block device (you could find some in /dev) 010 is a file 012 is a symlink .. (See list in precedent reply)