Linux the great

The  Users  utility allows you to view, modify, add, and delete local users in the graphical user interface. 3.2.1. Using the Users Settings Tool Press the  Super  key to enter the Activities Overview, type  Users  and then press  Enter . The  Users  settings tool appears. The  Super  key appears in a variety of guises, depending on the keyboard and other hardware, but often as either the Windows or Command key, and typically to the left of the Spacebar. Alternatively, you can open the  Users  utility from the  Settings  menu after clicking your user name in the top right corner of the screen. To make changes to the user accounts, first select the  Unlock  button and authenticate yourself as indicated by the dialog box that appears. Note that unless you have superuser privileges, the application will prompt you to authenticate as  root . To add and remove users, select the  + ...

While users can be either people (meaning accounts tied to physical users) or accounts that exist for specific applications to use, groups are logical expressions of organization, tying users together for a common purpose. Users within a group share the same permissions to read, write, or execute files owned by that group. Each user is associated with a unique numerical identification number called a  user ID  ( UID ). Likewise, each group is associated with a  group ID  ( GID ). A user who creates a file is also the owner and group owner of that file. The file is assigned separate read, write, and execute permissions for the owner, the group, and everyone else. The file owner can be changed only by  root , and access permissions can be changed by both the  root  user and file owner. Additionally, Red Hat Enterprise Linux supports  access control lists  ( ACLs ) for files and directories which allow permissions for specific us...

Red Hat Enterprise Linux uses the  Filesystem Hierarchy Standard  ( FHS ) file system structure, which defines the names, locations, and permissions for many file types and directories. The FHS document is the authoritative reference to any FHS-compliant file system, but the standard leaves many areas undefined or extensible. This section is an overview of the standard and a description of the parts of the file system not covered by the standard. Compliance with the standard means many things, but the two most important are compatibility with other compliant systems and the ability to mount a  /usr/  partition as read-only. This second point is important because the directory contains common executables and should not be changed by users. Also, since the  /usr/  directory is mounted as read-only, it can be mounted from the CD-ROM or from another machine via a read-only NFS mount. ⁠1.2.1. FHS Organization The directories and files noted her...

hwclock  is a utility for accessing the hardware clock, also referred to as the Real Time Clock (RTC). The hardware clock is independent of the operating system you use and works even when the machine is shut down. This utility is used for displaying the time from the hardware clock.  hwclock also contains facilities for compensating for systematic drift in the hardware clock. The hardware clock stores the values of: year, month, day, hour, minute, and second. It is not able to store the time standard, local time or Coordinated Universal Time (UTC), nor set the Daylight Saving Time (DST). The  hwclock  utility saves its settings in the  /etc/adjtime  file, which is created with the first change you make, for example, when you set the time manually or synchronize the hardware clock with the system time. NOTE In Red Hat Enterprise Linux 6, the  hwclock  command was run automatically on every system shutdown or reboot, bu...

The  date  utility is available on all Linux systems and allows you to display and configure the current date and time. It is frequently used in scripts to display detailed information about the system clock in a custom format. 2.2.1. Displaying the Current Date and Time To display the current date and time, run the  date  command with no additional command line options: date This displays the day of the week followed by the current date, local time, abbreviated time zone, and year. By default, the  date  command displays the local time. To display the time in UTC, run the command with the  --utc  or  -u  command line option: date --utc You can also customize the format of the displayed information by providing the  +" format "  option on the command line: date +" format " Replace  format  with one or more supported control sequences Table 2.1. Commonly Used Control Sequences ...