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Consolidating the foundation of Linux, basic cmds

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Command Interface

We can enter command interface via the following ways.

  1. Excute init 3 with root.

    init run at runlevel 3.

  2. Hotkey: Ctrl + ALt + F1/2/3/…

init

init is the first process, it commonly locates on /sbin/init, if kernel can’t find init, it will try to run /bin/sh, if the operation fails , the OS will fail to start successfully.

init has 7 runlevels, we can check the default runlevel and runlevels in /etc/inittab. As follows:

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# Default runlevel. The runlevels used are:
#   0 - halt (Do NOT set initdefault to this)
#   1 - Single user mode(root)
#   2 - Multiuser, without NFS (The same as 3, if you do not have networking)
#   3 - Full multiuser mode(standard runlevel)
#   4 - unused(secure mode)
#   5 - X11(user interface)
#   6 - reboot (Do NOT set initdefault to this)
#
id:5:initdefault:
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/etc - configuration file directory
/bin - command directory
/sbin -  management command directory
/usr/bin & /usr/sbin Other commands pre-installed on the system

Help Commands

This part is very important, we can learn all the commands with the following help commands.

man(manual)

man has 9 setctions, we can check them via man man, as follows:

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MANUAL SECTIONS
The standard sections of the manual include:

       1      User Commands

       2      System Calls

       3      C Library Functions

       4      Devices and Special Files

       5      File Formats and Conventions

       6      Games et. Al.

       7      Miscellanea

       8      System Administration tools and Daemons

       9      Kernel routines

Manual sections are used to distinguish different parameters. For example, when there is a parameter with the same name, that the category is different. we can specify by sections.

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man (1) man # default is 1

When we do not know the classification, all manuals can be got as follows.

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man -a passwd

help

Before introducing this command, we need to figure out two concepts. As follows:

  1. Builtin commands : come with shell.
  2. External commands : the others.

We can figure out what type a command belongs to depend on the following way:

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type <command>  # print the type of command

example:
[lee@lee-server bin]$ type ls
ls is aliased to `ls --color=auto'

[lee@lee-server bin]$ type cd
cd is a shell builtin

Different types of commands have different execution formats, as follows:
Builtin commands:

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help <command>
help cd

External commands:

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<command> --help
ls --help

info

info is more detailed command than help.

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info <command>
info ls

Basic commands

Switch Account

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su - <usr>

pwd

man pwd:

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NAME
       pwd - print name of current/working directory

SYNOPSIS
       pwd [OPTION]...

DESCRIPTION
       Print the full filename of the current working directory.

       -L, --logical
              use PWD from environment, even if it contains symlinks

       -P, --physical
              avoid all symlinks

       --help display this help and exit

       --version
              output version information and exit

       NOTE:  your  shell may have its own version of pwd, which Commonly supersedes the version described here.  Please refer to your shell’s
       documentation for details about the options it supports.

ls

Basic usage:

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[lee@lee-server bin]$ ls /home / /home/*
[sudo] password for lee: 
/:
bin  boot  dev	etc  home  lib	lost+found  media  misc  mnt  net  opt	proc  root  sbin  selinux  srv	sys  tmp  usr  var

/home:
lee  lost+found

/home/lee:
bin  blog  Desktop  Documents  Downloads  lee  mbr2.bin  mbr.bin  Music  Pictures  Public  script  server  Templates  Videos

/home/lost+found:

Common options:

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-a, --all
      do not ignore entries starting with .
-l    use a long listing format
-r, --reverse
      reverse order while sorting
-R, --recursive
      list subdirectories recursively
-t    sort by modification time

cd

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cd - # change to $(OLDPWD)

mkdir

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mkdir - Create the DIRECTORY(ies), if they do not already exist.
rmdir - Remove the DIRECTORY(ies), if they are empty.

Option:
-p, --parents   create/remove DIRECTORY and its ancestors; e.g., `mkdir/rmdir -p a/b/c' is
                    similar to `mkdir/rmdir a/b/c a/b a'

rm  - Remove (unlink) the FILE(s).

Option:
  -f, --force           ignore nonexistent files, never prompt
  -r, -R, --recursive   remove directories and their contents recursively

cp

Common options:

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-a, --archive
        same as -dR --preserve=all; 保留源文件所有信息
-p     same as --preserve=mode,ownership,timestamps; 保留源文件时间
-R, -r, --recursive
        copy directories recursively
-v, --verbose
        explain what is being done

cat

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cat - Concatenate FILE(s), or standard input, to standard output.

head - output the first part of files
        With no FILE, or when FILE is -, read standard input. 
    -n   output the fist n lines instead of the first 10(default value)

tail - output the last part of files
    -n  output the last n lines instead of the last 10(default value)
    -f  output appended data as the file grows, eg, get the logs.

wc - print newline, word, and byte counts for each file
    -l, --lines
        print the newline counts


more - More is a filter for paging through text one screenful at a time.
less

Compression and decompression

Common commands:

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# compression rate increases in turn.
tar 
gzip
bzip2

Commond suffix:

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.tar.gz 
.tar.bz2 
.tgz

Compress:

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tar -c  
tar czf ，integrate gzip，fast but low compression rate.  common suffix is '.tar.gz'
tar cjf , integrate bzip2 , slow but high compression rate. Common suffix is '.tar.bz2'

Extract:

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tar xf -C <out_dir> 
    zxf
    jxf

Wildcard

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*  any string
？ one char,  file? = filea, fileb  not fileab
[xyz]  one of xyz
[a~z]  range between a and z
[!xyz] or [^xyz] not one of xyz