courses under ccna

courses under ccna.This explains the situation that sometimes occurs when an administrator grants a user access to a file but not to theaccess to the directory where the file is located, so that the user with access rights cannot open the file. The reason for this is very simple.368 Chapter 9 Linux and macOS-based AnalysisThe user does not have access to the directory where the file is located and cannot even "enter" the directory.Another concept that needs to be introduced is the group of a file or directory, which is a collection of permissions for one or more users grouped together. When you create a user, you need to assign that user to a group. For example, all employees can be assigned to a group called employees, and all network operators to another group called administrators. This way, all users belonging to a group can be given the same level of permissions at once, rather than having to be assigned on a per-user basis. A user can belong to one or more groups. Figure 9.3 shows an example of executing the id command for user jomuniz, whose user ID is 501.J0MUNIZ-M-91SU:-jomuniz$ id uid=501(jomuniz) gid=20(staff) groups=20(staff),12(everyone),61(localaccounts),7 9(_appserverusr)r80(admin) ,81(_appserveradm),98(_lpadmin),33(_appstore),100(_lpo perator),204(_developer),395(com.apple.access_ftp),398(com.apple.access_ screensh aring),399(com.apFigure 9.3 Example of a user IDIf a user is the owner of a file and the user belongs to multiple groups, the user can execute the chgrp command to modify the file's genus group. Let's say that the command chgrp staff file.txt has the effect of changing the genus group of the file file.txt to the group 'staff'. Note that this command does not affect the file owner's ownership of the file, only the file owner can change the ownership of the file. The chgrp command can only modify the file's genus group, for example, the previous example grants the group 'staff' access to the file file.txt. To change the owner of a file, the chown command can be executed. For example, the chown Bob file.txt command can be executed to grant ownership of the file sentence e.txt to Bob0Sometimes, changing the group or owner of a file or directory requires superuser privileges, which are the highest level of access and should only be used in special circumstances (for example, when performing administrative tasks). Most UNIX distributions support the su (substitute user) command, which provides superuser privileges for normal users to perform certain "lite" tasks. When the su command is executed, you are prompted for the superuser's password. If the password passes, you will be given a shell with superuser privileges, and entering exit will revert back to the previous user privilege level.Distributions such as Ubuntu support the sudo command, which provides superuser privileges on demand. Typically, sudo is used to execute a specific command, i.e., you can type sudo whatever_command to execute