Why do i use sudo su to log in to root and always display command not found?

  html5, question

And I can log in with sudo -s? Thank you for your answer.

.bashrc:

# ~/.bashrc: executed by bash(1) for non-login shells.
 # see /usr/share/doc/bash/examples/startup-files (in the package bash-doc)
 # for examples
 
 #  If not running interactively, don't do anything
 [ -z "$PS1" ] && return
 
 # don't put duplicate lines or lines starting with space in the history.
 # See bash(1) for more options
 HISTCONTROL=ignoreboth
 
 # append to the history file, don't overwrite it
 shopt -s histappend
 
 # for setting history length see HISTSIZE and HISTFILESIZE in bash(1)
 HISTSIZE=1000
 HISTFILESIZE=2000
 
 # check the window size after each command and, if necessary,
 # update the values of LINES and COLUMNS.
 shopt -s checkwinsize
 
 # If set, the pattern "**" used in a pathname expansion context will
 # match all files and zero or more directories and subdirectories.
 #shopt -s globstar
 
 # make less more friendly for non-text input files, see lesspipe(1)
 [ -x /usr/bin/lesspipe ] && eval "$(SHELL=/bin/sh lesspipe)"
 
 # set variable identifying the chroot you work in (used in the prompt below)
 if [ -z "$debian_chroot" ] && [ -r /etc/debian_chroot ];  then
 debian_chroot=$(cat /etc/debian_chroot)
 fi
 
 # set a fancy prompt (non-color, unless we know we "want" color)
 case "$TERM" in
 xterm-color) color_prompt=yes;  ;
 esac
 
 # uncomment for a colored prompt, if the terminal has the capability;  turned
 # off by default to not distract the user: the focus in a terminal window
 # should be on the output of commands, not on the prompt
 #force_color_prompt=yes
 
 if [ -n "$force_color_prompt" ];  then
 if [ -x /usr/bin/tput ] && tput setaf 1 >&/dev/null;  then
 # We have color support;  assume it's compliant with Ecma-48
 # (ISO/IEC-6429). (Lack of such support is extremely rare, and such
 # a case would tend to support setf rather than setaf.)
 color_prompt=yes
 else
 color_prompt=
 fi
 fi
 
 if [ "$color_prompt" = yes ];  then
 PS1='${debian_chroot:+($debian_chroot)}\[\033[01;  32m\]\u@\h\[\033[00m\]:\[\033[01;  34m\]\w\[\033[00m\]\$ '
 else
 PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
 fi
 unset color_prompt force_color_prompt
 
 # If this is an xterm set the title to user@host:dir
 case "$TERM" in
 xterm*|rxvt*)
 PS1="\[\e]0;  ${debian_chroot:+($debian_chroot)}\u@\h: \w\a\]$PS1"
 ;  ;
 *)
 ;  ;
 esac
 
 # enable color support of ls and also add handy aliases
 if [ -x /usr/bin/dircolors ];  then
 test -r ~/.dircolors && eval "$(dircolors -b ~/.dircolors)" || eval "$(dircolors -b)"
 alias ls='ls --color=auto'
 #alias dir='dir --color=auto'
 #alias vdir='vdir --color=auto'
 
 alias grep='grep --color=auto'
 alias fgrep='fgrep --color=auto'
 alias egrep='egrep --color=auto'
 fi
 
 # some more ls aliases
 alias ll='ls -alF'
 alias la='ls -A'
 alias l='ls -CF'
 
 # Add an "alert" alias for long running commands.  Use like so:
 #   sleep 10;  alert
 alias alert='notify-send --urgency=low -i "$([ $?   = 0 ] && echo terminal || echo error)" "$(history|tail -n1|sed -e '\''s/^\s*[0-9]\+\s*//;  s/[;  &|]\s*alert$//'\'')"'
 
 # Alias definitions.
 # You may want to put all your additions into a separate file like
 # ~/.bash_aliases, instead of adding them here directly.
 # See /usr/share/doc/bash-doc/examples in the bash-doc package.
 
 if [ -f ~/.bash_aliases ];  then
 . ~/.bash_aliases
 fi
 
 # enable programmable completion features (you don't need to enable
 # this, if it's already enabled in /etc/bash.bashrc and /etc/profile
 # sources /etc/bash.bashrc).
 if [ -f /etc/bash_completion ] && !   shopt -oq posix;  then
 . /etc/bash_completion
 fi

Just su.
Sudo is not required for su command