Fedora web server - The three triads are read as follows: The
The three triads are read as follows: The first triad consists of the second, third, and fourth characters in thelong format file listing. This triad sets the permissions for the user,orowner,of the file. (Owners are discussed in the Beware of owners sec- tion, later in this chapter.) The second triad consists of the fifth, sixth, and seventh characters inthe long format file listing. This triad sets the permissions for the groupthat is assigned to the file. (Groups are discussed in the Hanging out ingroups section, later in this chapter.) The third triad consists of the eighth, ninth, and tenth characters in thelong format file listing. This triad sets the permissions for other,oreveryone who isn t the file s owner or a member of the owning group. Although each triad is often different from the others, the internal structureof each one is made up in the same way. Focus specifically on how to readone triad before looking at the set of them together. Each triad includes threecharacters: The first character is either an ror a dash. The rstands for read permis- sion. If ris set, the triad allows the entity it stands for (user, group, orother) to view the directory or file s contents. The second character is either a wor a dash. The wstands for writeper- mission. If wis set, the triad allows the entity it stands for to add or edititems to, or in, this directory or file. The third character is either an xor a dash. The xstands for executepermission. If xis set, the triad allows the entity it stands for to run programs contained in this directory or to run the particular program in this file. In all cases, if the dash sits in place of r, w, or x, the triad doesn t allow theentity the read, write, or execute permission. The following sections describe owners and groups in more detail. Beware of ownersYou may have noticed by now that I talk a great deal about owners (users) and groups in Linux. Every file and directory has both of these components: auser from the /etc/passwdfile that s assigned as its owner and a group from/etc/groupassigned as the group. Although an everyday user probably doesn t need to change file ownershipsoften, the root user does so regularly. If you add the file comments, for exam- ple, to /home/tomwhile you re logged on as the superuser(another term forthe administrator, who is the person who owns the root account), root ownsthat file. The user tomcan t do anything with it unless you have set the last212Part III:Getting Up to Speed with Linux