$ man man
$ man 1 man
$ man 7 man

$ man -k partition
$ man -k adduser
adduser (8)          - create a new user or update default new user information
$ man 8 adduser

$ date
Sun Nov 19 20:55:25 CST 2017
$ date +%x
11/19/2017
$ date +%R
20:57

$ file /etc
/etc: directory
$ file /etc/passwd
/etc/passwd: ASCII text

$ head /etc/passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
adm:x:3:4:adm:/var/adm:/sbin/nologin
lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
sync:x:5:0:sync:/sbin:/bin/sync
shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
halt:x:7:0:halt:/sbin:/sbin/halt
mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
operator:x:11:0:operator:/root:/sbin/nologin

$ head -n 3 /etc/passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin

$ tail /etc/passwd
pulse:x:171:171:PulseAudio System Daemon:/var/run/pulse:/sbin/nologin
gdm:x:42:42::/var/lib/gdm:/sbin/nologin
gnome-initial-setup:x:992:987::/run/gnome-initial-setup/:/sbin/nologin
sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
avahi:x:70:70:Avahi mDNS/DNS-SD Stack:/var/run/avahi-daemon:/sbin/nologin
postfix:x:89:89::/var/spool/postfix:/sbin/nologin
ntp:x:38:38::/etc/ntp:/sbin/nologin
tcpdump:x:72:72::/:/sbin/nologin
node3:x:1000:1000:node3:/home/node3:/bin/bash
named:x:25:25:Named:/var/named:/sbin/nologin

$ tail -n 3 /etc/passwd
tcpdump:x:72:72::/:/sbin/nologin
node3:x:1000:1000:node3:/home/node3:/bin/bash
named:x:25:25:Named:/var/named:/sbin/nologin

$ wc /etc/passwd
  41   79 2107 /etc/passwd
$ wc -l /etc/passwd
41 /etc/passwd
$ wc -w /etc/passwd
79 /etc/passwd
$ wc -c /etc/passwd
2107 /etc/passwd

# locate Kylin

# locate -i Kylin

# locate -i -n 1 Kylin
/home/kylin

# updatedb

# find / -name sshd_config
# find / -name '*.txt'
# find /etc -name '*pass*'

find / -user kylin

# find / -iname '*messages*'

# find / -size 10M
# find / -size +10G
# find / -size -10k

# find / -mmin 120
# find / -mmin +120
# find / -mmin -120

# find /home -perm 764

# find /etc/ -type d
# find /etc/ -type f
# find / -type l
# find /dev/ -type b

# find / -type f -links +1

$ env
....