multiuser system, so multitasking
multichoice system: Bourne shell, C shell, and Korn shell
what is shell?
in UNIX, the command-line user interface is called a shell
$ passwd
who are you?
$ whoami
$ who am i
$ id
finding out what other users are logged into the system
$ users
$ who
what is everyone doing on the computer?
$ w
11:49am up 920 day(s), 18:24, 3 users, load average: 0.27, 0.34, 0.34
User tty login@ idle JCPU PCPU what
...
the user's login name
the name of the tty the user is on
the time of day the user logged on(in hours:minutes)
the idle time-that is
the number of minutes since the user last typed anything (in hours:minutes)
the CPU time used by all processes and their children on that terminal (in minutes:seconds)
the CPU time used by the currently active processes (in minutes:seconds)
the name and arguments of the current process
$ w
-h Suppress the heading.
-l Produce a long form of output, which is the default.
-s Produce a short form of output. In the short form, the tty is abbreviated, the login time and CPU times are left off, as are the arguments to commands.
-u Produces the heading line which shows the current time, the length of time the system has been up, the number of users logged into the system, and the aver- age number of jobs in the run queue over the last 1, 5 and 15 minutes.
-w Produces a long form of output, which is also the same as the default.
-s -u
$ w -u
$ uptime
$ procinfo (linux)
checking the current date and time
$ date
looking at a calendar
$ cal
$ cal 2 1985
$ cal 1985
(from A.D.0)
Using bc infix calculator
$ bc
1+1
2
quit
$ bc -l math
$ bc -l
ctrl+d
Moving about the File System
anything is not a folder is a file.
The top level of the UNIX file structure (/) is known as the root directory or slash directory,
and it always has a certain set of subdirectories, including bin, dev, etc, lib, mnt, tmp, and usr.
/bin,/sbin,usr/bin, -->executable binaries
/dev -->device drivers
/etc -->administrative files and information
/lib
/lost+found
/mnt -->a common place to mount external media—hard disks, removable cartridge drives
/sys -->contains files indicating the system configuration
/tmp -->fastest
/usr -->this directory was intended to be the central storage place for all user-related commands
A hidden file is any file with a dot as the first character of the filename.
See also dot files.
Preference file:These are what dot files (hidden files) really are: They contain your individual preferences for many of the UNIX commands you use.
UNIX uses an ordered list of directories called a search path for this purpose. The search path typically lists five or six different directories on the system where the computer checks for any application you request.
The question arises: What happens if your own personal copy of an application has the same name as a standard system application? The answer is that the system always finds the standard application first, if its directory is listed earlier in the search path.
$ env
$ echo $PATH
$ echo $HOME