Three. Shell Basics 2

I. User and user group management < A; user classification: Because of different roles, permissions and tasks that are completed are different.          The user's role is identified by UID, and the UID of the user is globally unique. 1 . Root User: The system is unique, is real, can log on the system, can be operating system any file and command, with the highest authority; 2. Virtual User: Distinguished from real users, such users do not have the ability to log on to the system, but the system is indispensable to the operation of users, such as bin, daemon, ADM, ftp, mail, etc., such users are owned by the system itself, not later added, of course, we can also add virtual users; 3. Normal User: This type of user can log in to the system, but only the contents of its root directory, permissions are restricted, such users are added by the system administrator;     < two >  user management commands:          1. Add Users: Useradd (or AddUser)                        & nbsp 2. Modify user:usermod                         3. Delete User: Userdel&nbs P                                 &NBSP ; 4. Password Management:passwd                    < three > user Group Management     &NBSP ;     User group: Is the collective of users with the same characteristics, users and user groups of the relationship is many-to-many, a user can belong to multiple user groups, similarly, a user group can contain multiple users;          Common commands:          1.groupadd  2.groupmod   3.groupdel          &N Bsp         two. Files and directories      < >linux directory structure           1. /     :linux mostThe outer directory, root directory;     2.bin    : Executable application directory;     3.boot  : Start required files;     4.dev:    &NBSP;5.ETC  : A directory of system configuration information;     6.home: directory where user information is stored;     7.lib   &NBSP: library file directory;    &NBSP;8.MNT  : Managing information on mounted disks, USB drives, etc.;     9.opt  : & nbsp    10.root:root user's root directory;     11.usr:     12.var: variable, such as a log;          < two > Common commands:    &NBSP;1.LS: List information about files and subdirectories below the directory;        usage: ls[ option] [file or directory]        (1) ls-a: Can show hidden files         (2) Ls-l: Show detailed directory information ; "Equivalent to: LL"     &NBSP;2.CP: Copy File command:        usage: cp[option] [source] [destination]    & nbsp;    (1). cp-a source File destination directory      cp -a the file permissions and modification dates of the copy are not changed      (2). cp-r source File destination directoryCp-r can copy the entire directory 3.mv:4.rmv:5.mkdir:6.rmdir:7.cd: < three;. File and directory Rights Management 1. Each file and directory in the Linux system has access permission to determine how the user can access and manipulate the files and directories; 2. Explanation: As shown: There are two types of identities before the permission group:-and D-Indicates that this is a file; D means that this is a folder; "That is dire     Ctory's abbreviation "3. Common commands: (1) chmod: (2) Chown: (3) Find:linux system to find files, find command to help users in the daily use of Linux management, to find out the user's needs of the files. find [path] [options] [action] three. vi File Editor:

Three. Shell Basics 2