shutdown 
85:~# shutdown -- help
Usage:    shutdown [-akrhHPfnc] [-t secs] time [warning message]
                  -a:      use /etc/shutdown.allow
                  -k:      don't really shutdown, only warn.
                  -r:      reboot after shutdown.
                  -h:      halt after shutdown.
                  -P:      halt action is to turn off power.
                  -H:      halt action is to just halt.
                  -f:      do a 'fast' reboot (skip fsck).
                  -F:      Force fsck on reboot.
                  -n:      do not go through "init" but go down real fast.
                  -c:      cancel a running shutdown.
                  -t secs: delay between warning and kill signal.
                  ** the "time" argument is mandatory! (try "now") **
uptime 
85:~# uptime
 12:54:19 up  2:16,  1 user,  load average: 0.01, 0.01, 0.00
whatis = display manual page descriptions 
85:~# whatis pwd
pwd (1)              - print name of current/working directory
root@debian:~# find / -name 'sip.conf' - to find any kind of file (not just program files) anywhere on the hard-drive (not just in the path)
whereis = locate the binary, source, and manual page files for a command 
mc: /usr/bin/mc /etc/mc /usr/lib/mc /usr/share/mc /usr/share/man/man1/mc.1.gz
85:~# whereis apt-get
apt-get: /usr/bin/apt-get /usr/share/man/man8/apt-get.8.gz
85:~# type traceroute traceroute is /usr/bin/traceroute
crontab = file named dato/root/anotheruther in /var/spool/cron/crontabs directory
daemon named crontd regulary reads this file and executes 
usage:  crontab [-u user] file
        crontab [-u user] { -e | -l | -r }
                (default operation is replace, per 1003.2)
        -e      (edit user's crontab)
        -l      (list user's crontab)
        -r      (delete user's crontab)
#apt-get remove vhcs - to remove package
# apt-get --purge remove vim.tiny - to remove package completely, including configuration files

root@debian:/home/kote# update-alternatives --config editor There are 2 choices for the alternative editor (providing /usr/bin/editor). Selection Path Priority Status ------------------------------------------------------------ 0 /bin/nano 40 auto mode 1 /bin/nano 40 manual mode * 2 /usr/bin/mcedit 25 manual mode Press enter to keep the current choice[*], or type selection number:

source ~/.bashrc - to reload .bashrc (after editing):

root@debian:/etc/asterisk# source ~/.bashrc root@debian:/etc/asterisk#

cd ~/ - go to corresponding user's home directory
root@debian:/# passwd users_name - change password of the user called users_name
userdel users_name - delete user
TCP Wrappers Configuration Files When a client request is received by a TCP wrapped service, it takes the following basic steps:

  1. The service references /etc/hosts.allow. — The TCP wrapped service sequentially parses the /etc/hosts.allow file and applies the first rule specified for that service. If it finds a matching rule, it allows the connection. If not, it moves on to step 2.

  2. The service references /etc/hosts.deny. — The TCP wrapped service sequentially parses the /etc/hosts.deny file. If it finds a matching rule is denies the connection. If not, access to the service is granted.

Or, one can put all rules in 1 File
sshd : client-1.example.com : allow
sshd : client-2.example.com : deny
By allowing access control on a per-rule basis, the option field allows administrators to consolidate all access rules into a single file: either hosts.allow or hosts.deny. Some consider this an easier way of organizing access rules.

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