Introduction to Linux

# apt-get update    # yum makecache
Hit:1 https://deb.nodesource.com/node_8.x stretch InRelease
Hit:2 https://download.docker.com/linux/debian stretch InRelease
...
Reading package lists... Done
# apt-cache search nginx    # yum search
nginx-small, powerful, scalable web/proxy server
# apt-cache madison nginx   # yum --showduplicates search nginx
nginx| 1.13.3-1~bpo9+1 | http://mirrors.163.com/debian stretch-backports/main amd64 Packages
nginx| 1.10.3-1+deb9u1 | http://mirrors.163.com/debian stretch/main amd64 Packages
# apt-get install nginx     # yum install nginx
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
...

apt-get update             ->  apt update
apt-get upgrade            ->  apt upgrade
apt-get dist-upgrade       ->  apt full-upgrade
apt-get install package    ->  apt install package
apt-get remove package     ->  apt remove package
apt-get autoremove         ->  apt autoremove
apt-cache search string    ->  apt search string
apt-cache policy package   ->  apt list -a package
apt-cache show package     ->  apt show package
apt-cache showpkg package  ->  apt show -a package

$ touch hello.sh
$ cat <<EOF
> #!/bin/bash
>
> echo "Hello GNU/Linux!"
> EOF
#!/bin/bash
echo "Hello GNU/Linux!"
$ /bin/bash hello.sh
Hello GNU/Linux!
$ chmod +x hello.sh
$ ./hello.sh
Hello GNU/Linux!
$

$ cat hello.sh
#!/bin/bash
greeting="Hello GNU/Linux!"
$ ./hello.sh
$ echo $greeting
...
$ . ./hello.sh   # source ./hello.sh
$ echo $greeting
Hello GNU/Linux!

$ greeting="Hello GNU/Linux!"
$ echo $greeting
Hello GNU/Linux!
$ vi hello.sh
$ cat hello.sh
#!/bin/bash
echo $greeting
$ ./hello.sh
$ export greeting
$ ./hello.sh
Hello GNU/Linux!

# mkdir mydir
# touch myfile
# ln -sf myfile mylink
# ls -l
total 4
drwxr-xr-x 2 root root 4096 Sep 10 17:10 mydir
-rw-r--r-- 1 root root 0 Sep 10 17:10 myfile
lrwxrwxrwx 1 root root 6 Sep 10 17:10 mylink-> myfile
# ls -l /var/run/*.sock
srw-rw---- 1 root docker 0 Sep 10 11:01 /var/run/docker.sock
# ls -l /dev/sda1
brw-rw---- 1 root disk 8, 1 Sep 10 11:01 /dev/sda1
# ls -l /dev/tty1
crw--w---- 1 root tty 4, 1 Sep 10 11:01 /dev/tty1

/tmp$ df -h
Filesystem      Size    Used    Avail     Use%   Mounted on
udev            986M       0    986M        0%   /dev
tmpfs           200M    6.1M    194M        4%   /run
/dev/sda1        19G    9.9G    7.9G       56%   /
tmpfs           998M       0    998M        0%   /dev/shm
tmpfs           5.0M       0    5.0M        0%   /run/lock
tmpfs           998M       0    998M        0%   /sys/fs/cgroup
tmpfs           200M       0    200M        0%   /run/user/1000
/tmp$ df . -h
Filesystem      Size    Used    Avail     Use%   Mounted on
/dev/sda1        19G    9.9G    7.9G       56%   /
/tmp$ touch foobar
/tmp$ ls -li foobar
262826 - rw-r--r-- 1 x x 0 Sep 11 21:01 foobar

/tmp# mkdir mydir   # make a directory
/tmp# cd mydir/     # change to mydir/
/tmp/mydir# pwd     # print the work directory
/tmp/mydir
/tmp/mydir# touch myfile    # make a file
/tmp/mydir# ls      # list the currentydirectory contents
myfile
/tmp/mydir# mv myfile myfile2   # rename myfileto myfile2
/tmp/mydir# rm myfile2          # remove myfile2
/tmp/mydir# cd ..               # change to parent dir
/tmp# rm -r mydir/              # remove mydir
/tmp# ls
/tmp#
/tmp# cat <<EOF > foo
> Hello GNU/Linux!
> EOF
/tmp# cat foo
Hello GNU/Linux!
/tmp# cp foo bar    # copy foo to bar
/tmp# ls
bar foo
/tmp# cat bar
Hello GNU/Linux!
/tmp# mkdir mydir
/tmp# mv foo bar mydir/     # move foo bar to mydir/
/tmp# ls
mydir
/tmp# cp -a mydir/ mydir2   # copy mydir/ to mydir2
/tmp# ls
mydir mydir2

/tmp# cat <<EOF > hello.sh
> #!/bin/bash
> echo "Hello GNU/Linux!"
> EOF
/tmp# ls -l
total 4
-rw-r--r-- 1 root root 36 Sep 10 17:34 hello.sh
/tmp# chmod +x hello.sh
/tmp# ls -l
total 4
-rwxr-xr-x 1 root root 36 Sep 10 17:34 hello.sh
/tmp# ./hello.sh
Hello GNU/Linux!
/tmp# stat -c "%a" hello.sh
755
/tmp# chmod 777 hello.sh
/tmp# ls -l
total 4
-rwxrwxrwx 1 root root 36 Sep 10 17:34 hello.sh
/tmp# tail -n 1 hello.sh
echo "Hello GNU/Linux!"
/tmp# head -n 1 hello.sh
#!/bin/bash
/tmp# cat hello.sh
#!/bin/bash
echo "Hello GNU/Linux!"

/bin    Common programs, shared by the system, the system administrator and the users.
/boot   The startup files and the kernel, vmlinuz.
/dev    Contains references to all the CPU peripheral hardware, which are represented as files with special properties.
/etc    Most important system configuration files are in /etc, this directory contains data similar to those in the Control Panel in Windows
/home   Home directories of the common users.
/lib    Library files, includes files for all kinds of programs needed by the system and the users.
/mnt    Standard mount point for external file systems, e.g. a CD-ROM or a digital camera.
/opt    Typically contains extra and third party software.
/proc   A virtual file system containing information about system resources.
/root   The administrative user's home directory.
/sbin   Programs for use by the system and the system administrator.
/tmp    Temporary space for use by the system, cleaned upon reboot, so don't use this for saving any work!
/usr    Programs, libraries, documentation etc. for all user-related programs.
/var    Storage for all variable files and temporary files created by.

$ ps -f -C nginx
UID        PID  PPID  C STIME TTY          TIME CMD
root      3972  3957  1 16:18 ?        00:00:00 nginx: master process nginx -g daemon off;
systemd+  4012  3972  0 16:18 ?        00:00:00 nginx: worker process

$ ps aux|grep nginx
root      3972  0.3  0.2  32424  4872 ?        Ss   16:18   0:00 nginx: master process nginx -g daemon off;
systemd+  4012  0.0  0.1  32912  2492 ?        S    16:18   0:00 nginx: worker process
x         4026  0.0  0.0  12784   948 pts/2    S+   16:19   0:00 grep --color=auto nginx

$ ps -f -u www-data
UID        PID  PPID  C STIME TTY          TIME CMD
www-data  6631  6630  0 21:43 ?        00:00:00 nginx: worker process
www-data  6632  6630  0 21:43 ?        00:00:00 nginx: worker process

$ pstree -p
systemd(1)─┬─acpid(422)
           ├─agetty(435)
           ├─cron(354)
           ├─dbus-daemon(360)
           ├─dhclient(477)
           ├─irqbalance(358)
           ├─ntpd(446)───{ntpd}(455)
           ├─rsyslogd(359)─┬─{in:imklog}(403)
           │               ├─{in:imuxsock}(402)
           │               └─{rs:main Q:Reg}(404)
           ├─sshd(353)───sshd(1360)───sshd(1369)───bash(1370)───pstree(3168)
           ├─systemd(1362)───(sd-pam)(1363)
           ├─systemd-journal(197)
           ├─systemd-logind(417)
           └─systemd-udevd(211)

# pstree -p
init(1)─┬─acpid(2155)
        ├─auditd(2052)─┬─audispd(2054)───{audispd}(2055)
        │              └─{auditd}(2053)
        ├─dhclient(2001)
        ├─events/0(4)

        ├─klogd(2087)
        ├─ksoftirqd/0(3)
        ├─kthread(6)─┬─aio/0(245)
        │            ├─ata/0(498)

        ├─smartd(2338)
        ├─sshd(2244)───sshd(2395)───sshd(2402)───bash(2403)───su(2435)───bash(2436)───pstree(2519)
        ├─syslogd(2084)
        └─udevd(575)

$ touch foo
$ sudo touch bar
$ ls -l
total 0
-rw-r--r-- 1 root root 0 Sep 11 21:57 bar
-rw-r--r-- 1 x    x    0 Sep 11 21:57 foo
$ chown x bar
chown: changing ownership of 'bar': Operation not permitted
$ sudo chown x bar
$ ls -l
total 0
-rw-r--r-- 1 x root 0 Sep 11 21:57 bar
-rw-r--r-- 1 x x    0 Sep 11 21:57 foo
$ sudo chgrp x bar
$ ls -l
total 0
-rw-r--r-- 1 x x 0 Sep 11 21:57 bar
-rw-r--r-- 1 x x 0 Sep 11 21:57 foo$

$ ps -f -C nginx,ps
UID        PID  PPID  C STIME TTY          TIME CMD
root      6630     1  0 21:43 ?        00:00:00 nginx: master process nginx
www-data  6631  6630  0 21:43 ?        00:00:00 nginx: worker process
www-data  6632  6630  0 21:43 ?        00:00:00 nginx: worker process
x         6872  3315  0 22:02 pts/1    00:00:00 ps -f -C nginx,ps
$ sudo touch foobar
[sudo] password for x:
$ echo 'Hello GNU/Linux!' > foobar
-bash: foobar: Permission denied
$ ls -l foobar
-rw-r--r-- 1 root root 0 Sep 12 13:56 foobar
$ su
Password:
# echo 'Hello GNU/Linux!' > foobar
# exit
exit
$ id
uid=1000(x) gid=1000(x) groups=1000(x),24(cdrom),25(floppy),27(sudo),29(audio),30(dip),44(video),46(plugdev),108(netdev),999(docker)
$ sudo grep '%sudo' /etc/sudoers
%sudo   ALL=(ALL:ALL) ALL$

~# cd ~xianyu
-su: cd: ~xianyu: No such file or directory
~# useradd -s /bin/bash -u 2000 -c "Hello GNU/Linux!" -m xianyu
~# cd ~xianyu/
/home/xianyu# grep 'xianyu' /etc/passwd
xianyu:x:2000:2000:Hello GNU/Linux!:/home/xianyu:/bin/bash
/home/xianyu# id xianyu
uid=2000(xianyu) gid=2000(xianyu) groups=2000(xianyu)
/home/xianyu# su - xianyu
~$ pwd
/home/xianyu
~$ exit
logout
/home/xianyu# cd
~# userdel -r xianyu
userdel: xianyu mail spool (/var/mail/xianyu) not found
~# cd ~xianyu
-su: cd: ~xianyu: No such file or directory

Symbolic Notation   Numeric Notation    English
----------          0000                no permissions
-rwx------          0700                read, write, & execute only for owner
-rwxrwx---          0770                read, write, & execute for owner and group
-rwxrwxrwx          0777                read, write, & execute for owner, group and others SECURITY RISK
---x--x--x          0111                execute
--w--w--w-          0222                write
--wx-wx-wx          0333                write & execute
-r--r--r--          0444                read
-r-xr-xr-x          0555                read & execute
-rw-rw-rw-          0666                read & write
-rwxr-----          0740                owner can read, write, & execute; group can only read; others have no permissions

$ kill -l
 1) SIGHUP          2) SIGINT(Ctrl-C)      3) SIGQUIT(Ctrl-\)    4) SIGILL            5) SIGTRAP
 6) SIGABRT         7) SIGBUS              8) SIGFPE             9) SIGKILL          10) SIGUSR1
11) SIGSEGV        12) SIGUSR2            13) SIGPIPE           14) SIGALRM          15) SIGTERM
16) SIGSTKFLT      17) SIGCHLD            18) SIGCONT           19) SIGSTOP(Ctrl-Z)  20) SIGTSTP
21) SIGTTIN        22) SIGTTOU            23) SIGURG            24) SIGXCPU          25) SIGXFSZ
26) SIGVTALRM      27) SIGPROF            28) SIGWINCH          29) SIGIO            30) SIGPWR
31) SIGSYS         34) SIGRTMIN           35) SIGRTMIN+1        36) SIGRTMIN+2       37) SIGRTMIN+3
38) SIGRTMIN+4     39) SIGRTMIN+5         40) SIGRTMIN+6        41) SIGRTMIN+7       42) SIGRTMIN+8
43) SIGRTMIN+9     44) SIGRTMIN+10        45) SIGRTMIN+11       46) SIGRTMIN+12      47) SIGRTMIN+13
48) SIGRTMIN+14    49) SIGRTMIN+15        50) SIGRTMAX-14       51) SIGRTMAX-13      52) SIGRTMAX-12
53) SIGRTMAX-11    54) SIGRTMAX-10        55) SIGRTMAX-9        56) SIGRTMAX-8       57) SIGRTMAX-7
58) SIGRTMAX-6     59) SIGRTMAX-5         60) SIGRTMAX-4        61) SIGRTMAX-3       62) SIGRTMAX-2
63) SIGRTMAX-1     64) SIGRTMAX

$ ls -l /dev/std*
lrwxrwxrwx 1 root root 15 Sep 12 09:28 /dev/stderr -> /proc/self/fd/2
lrwxrwxrwx 1 root root 15 Sep 12 09:28 /dev/stdin -> /proc/self/fd/0
lrwxrwxrwx 1 root root 15 Sep 12 09:28 /dev/stdout -> /proc/self/fd/1
$ ls -l /proc/self/fd/{0,1,2}
lrwx------ 1 x x 64 Sep 12 20:15 /proc/self/fd/0 -> /dev/pts/0
lrwx------ 1 x x 64 Sep 12 20:15 /proc/self/fd/1 -> /dev/pts/0
lrwx------ 1 x x 64 Sep 12 20:15 /proc/self/fd/2 -> /dev/pts/0

$ cat hello.sh
#!/bin/bash
echo "Hello GNU/Linux!"
foo bar
$ ./hello.sh
Hello GNU/Linux!
./hello.sh: line 3: foo: command not found
$ ./hello.sh 2> err 1> out
$ cat err
./hello.sh: line 3: foo: command not found
$ cat out
Hello GNU/Linux!
$ ./hello.sh > allblue 2>&1
$ cat allblue
Hello GNU/Linux!
./hello.sh: line 3: foo: command not found
$ cat < out | xargs echo
Hello GNU/Linux!

$ man 1 man | less
$ git rebase –-help | more

" Display line number
set number

" Disable VIM swap and backup
set nobackup
set nowritebackup
set noswapfile

" Indenting source code
set expandtab
set tabstop=4
set shiftwidth=4

autocmd FileType make setlocal noexpandtab
autocmd FileType js   set shiftwidth=2

" UTF-8
set encoding=utf-8
set fileencoding=utf-8
set fileencodings=ucs-bom,utf-8,chinese
set ambiwidth=double

" syntax
syntax on

set showmatch

" backspace

set backspace=indent,eol,start