Detecting if another user is connected on UNIX systems

How to detect if another user is connected to your machine or your server? You can use the command “users” to check yourself is someone is connected. But to do it automatically, you’ll have to use some pipe :

expr length "`users | sed -e "s/\($USER\|\[ \]*\)//ig"`"

The first thing executed by the shell will be the thing under french apostrophe ( ` ). Theses are for evaluation a command, and replace it by what it outputs (normally print on the screen). The command users print the list of connected users into a pipe, to sed which evaluate its command as a regular expression (-e parameter). The command is “s” for substitute, and the rest tells him to find “$USER” (replaced by the currently connected user, you) and spaces and replace them by … nothing. So this part will be an empty string if there is no other users connected than “$USER” and something not empty if there is.

The “expr length” return the length of a string. So this commands print 0 if there is no other user connected, and >0 if there is some !

In a shell script to do something if yes or no…

usersstripped=`users | sed -e "s/\(tom\|\[ \]*\)//ig"`
connected=`expr length "$usersstripped"`
if [ "$connected" -eq "0" ] ; then
echo "No other user is connected"
echo "Other user connected !"

It is essentially the same command but done in two times, as in a shell script this command would not be evaluated correctly.

And if you want to put that in a cron to eg. send you a mail, you just have to type “crontab -e” and put a line like :

* * * * * /home/tom/connected

To launch it every minutes. But if you do that you’d better do something like detecting a connection…


To gain a lot of time, you can replace the old “bash” by “zsh”, which is a very more powerful shell with autocompletion, but not only… It has a configuration file called “.zshrc” that you have to put in your home. You can try zsh by installing it and typing “zsh”, and if you’re convinced, keeping it by typing chsh and choosing /bin/zsh.

You have my entire .zshrc but I choose 3 snippets that I prefer to show you the usefullness :

As I use Fedora, Debian, and Ubuntu, I made this to type “i program” to install profram on any system, and “u” to update the system. 

#i for install, u for update

if [ -e /bin/yum ]; then
alias i="sudo yum install"
alias u="sudo yum update"
alias i="sudo apt-get install"
alias u="sudo apt-get update && sudo apt-get dist-upgrade"

Force sudo for commands that anyway need it

alias yum="sudo yum"
alias apt-get="sudo apt-get"
alias service="sudo service"


Setting vi as default editor :

export EDITOR="vi"


The multiples ssh shorcuts

alias sshd="ssh -X"
alias sshc="ssh -X -L 3129:localhost:3129"

I use my zshrc on multiple system and multiple environment, hence you have some tricks and multiplications like different variables for the same program in the path variable.

#Using color schemes
autoload -U colors && colors

#Adding ADB to path variable
export PATH=${PATH}:/usr/src/android-sdk-linux/platform-tools/:/usr/src/android-sdk-linux/tools/:/opt/android/platform-tols/

# Aliases
#SSH shorcuts
alias sshd="ssh -X"
alias sshc="ssh -X -L 3129:localhost:3129"
alias ssha="ssh -X"
alias sshu="ssh -X"
alias sshq="ssh -X"
alias scpi="scp -i /home/tom/.ssh/id_rsa"
alias scp3="scp -P 3690 -i /home/tom/.ssh/id_rsa"
alias sam="ssh-add /home/tom/.ssh/id_rsa.montefiore"

#I have all my usefull scripts on my server itstudents, this alias update all scripts on a client, including this .zshrc
alias us="mkdir -p /home/tom/.scripts && scpi /home/tom/.ssh/authorized_keys && scpi /home/tom/.zshrc && scpi -r /home/tom/ && source /home/tom/.zshrc"

#Alias for these scripts...
#Archiver pack a folder in tar.gz
alias archiver="/home/tom/.scripts/archiver"
#Archiver7 pack a folder in a tar.7z
alias archiver7="/home/tom/.scripts/archiver7"
#Update and reset permissions of an svn
alias svnup="/home/tom/.scripts/svnup"
#Push an rsa key to the list of authorized keys
alias pushrsa="ssh \"cat - >> /home/tom/.ssh/authorized_keys\" < "

#Mount some local shares
alias mh="sudo mount -t nfs debserver:/home/tom /mnt/debserver-home"
alias mp="sudo mount -t nfs debserver:/pub /mnt/debserver-pub"

#Force sudo for some sudo-only commands like installers
alias yum="sudo yum"
alias apt-get="sudo apt-get"
alias service="sudo service"

#Some copy-pasted shorcut from elsewhere
alias k='tree'
alias ltr='ls -ltr'
alias r='screen -D -R'
alias ls='ls --color'
alias l='ls -lh'
alias ll='ls -la'
#i for install, u for update
if [ -e /bin/yum ]; then
alias i="sudo yum install"
alias u="sudo yum update"
alias i="sudo apt-get install"
alias u="sudo apt-get update && sudo apt-get dist-upgrade"

#Some links to launch programs on my android devices
alias adbf="ard && adb forward tcp:8999 tcp:8999 && google-chrome http://localhost:8999 &"
alias agmail="adb shell am start -a android.intent.action.MAIN -n"
alias amail="adb shell am start -a android.intent.action.MAIN -n"
alias ard="adb shell am start -a android.intent.action.MAIN -n net.xdevelop.rm/.RemoteMobile"
alias rr="sudo route del default && sudo route add default gw"

#Wake on lan shorcuts
alias wdebian="sudo etherwake 8C:89:A5:C1:D2:8A"



# Meta-u to chdir to the parent directory
bindkey -s '\eu' '^Ucd ..; ls^M'

bindkey '\e[1~' beginning-of-line
bindkey '\e[4~' end-of-line
bindkey '\e[7~' beginning-of-line
bindkey '\e[8~' end-of-line
bindkey '\eOH' beginning-of-line
bindkey '\eOF' end-of-line
bindkey '\e[H' beginning-of-line
bindkey '\e[F' end-of-line
bindkey '\e[5~' beginning-of-history
bindkey '\e[6~' end-of-history
bindkey '\e[3~' delete-char

#Enable auto correct for commands
setopt correct

# Pipe the current command through less
bindkey -s "\el" " 2>&1|less^M"
zstyle ':completion:*:(all-|)files' ignored-patterns '(|*/)CVS'
zstyle ':completion:*:cd:*' ignored-patterns '(*/)#CVS'

#Mode verbose pour cp, rm, chmod, chown et rename
for c in cp rm chmod chown rename; do
alias $c="$c -v"

#Pendunt une complétion affiche les points
expand-or-complete-with-dots() {
echo -n "\e[31m......\e[0m"
zle expand-or-complete
zle redisplay
zle -N expand-or-complete-with-dots
bindkey "^I" expand-or-complete-with-dots

setopt NO_BEEP
export EDITOR="vi"
setopt ZLE
setopt AUTO_CD

# Completion Stuff
bindkey -M viins '\C-i' complete-word

# Faster! (?)
zstyle ':completion::complete:*' use-cache 1
# generate descriptions with magic.
zstyle ':completion:*' auto-description 'specify: %d'

# Don't prompt for a huge list, page it!
zstyle ':completion:*:default' list-prompt '%S%M matches%s'

# Don't prompt for a huge list, menu it!
zstyle ':completion:*:default' menu 'select=0'

# Have the newer files last so I see them first
zstyle ':completion:*' file-sort modification reverse

# color code completion!!!! Wohoo!
zstyle ':completion:*' list-colors "=(#b) #([0-9]#)*=36=31"


# Separate man page sections. Neat.
zstyle ':completion:*:manuals' separate-sections true

# Egomaniac!
zstyle ':completion:*' list-separator 'fREW'

# complete with a menu for xwindow ids
zstyle ':completion:*:windows' menu on=0
zstyle ':completion:*:expand:*' tag-order all-expansions

# more errors allowed for large words and fewer for small words
zstyle ':completion:*:approximate:*' max-errors 'reply=( $(( ($#PREFIX+$#SUFFIX)/3 )) )'

# Errors format
zstyle ':completion:*:corrections' format '%B%d (errors %e)%b'

# Don't complete stuff already on the line
zstyle ':completion::*:(rm|vi):*' ignore-line true

# Don't complete directory we are already in (../here)
zstyle ':completion:*' ignore-parents parent pwd

zstyle ':completion::approximate*:*' prefix-needed false


export GREP_COLOR=31
alias grep='grep --color=auto'

#{{{ Prompt!

jobs_total="%(1j.${jobs_prompt1}${jobs_prompt2}${jobs_prompt3} .)"
error_total="%(?..${error_prompt1}${error_prompt2}${error_prompt3} )"

case "$TERM" in
function precmd() { print -Pn "\033]0;S $TTY:t{%100<...<%~%<<}\007" }
directory_prompt="%{$fg[$directory_color]%}%~%{$reset_color%} "
directory_prompt="%{$fg[$directory_color]%}%~%{$reset_color%} "

if [[ $USER == root ]]; then
PS1="${host_prompt} ${jobs_total}${history_total} ${error_total}${post_prompt} "
RPROMPT="%{$fg_bold[$user_color]%}<%{$reset_color%} ${directory_prompt}${fg_light_gray}[%*]%{$reset_color%}"
#Type f to flush the console to history file
alias f="fc -W"



#Append to history file instead of re-writing

#To share history between terminal, not what I want as I always have multiple terminals like one for generating packet, the other to receive them

#Remove blanks
setopt hist_reduce_blanks
#Remove duplicates
setopt hist_ignore_all_dups
#Do not store commands in history starting with white space
setopt hist_ignore_space

autoload -U compinit promptinit zcalc zsh-mime-setup

Wanscam IP Camera Update

As IP Camera are cheaper than real alarm, I decided to buy a cheap IP Camera like ones you see for 50€ when typing “ip camera” on amazon :

(Re)brand : Wanscam
Model : FR4020A2
Original system firmware  :
Original WEB UI :


It can detect movement, move horizontally and vertically by a web interface, send mail, send image on ftp, etc etc…

But the reference nearly doesn’t exist, and finding a newer firmware is nearly impossible. But this camera looks a lot like a lot of others, including Foscam. So I decided to find a newer firmware for similar webcams. I found that the firmware for mine was named lr_cmos_0_X_Y_Z.bin, and I searched for newer version. I finaly came acrosse this page : where a link to a firmware for the Dericam M801W is given containing a file named “lr_cmos_0_41_2_51.bin”, I decided to flash it and… It works ! It doesn’t seem that there exist any newer firmware…

About the web ui firmware, I searched for a firmware in the web coming with the system firmware around 41.2.51, and I came accross,128.0.html#msg1956 . The web ui firmware number is smaller but  clearly, the interface is newer… It comes with something we can call a “design”, far away from the horrible original nearly “text only” interface.

So my final versions are :

  Device Firmware Version
  Device Embeded Web UI Version

You can download the files here : lr_cmos_0_41_2_51 (flash the lr_cmos first!) and WEB UI The video quality is really better ! Wifi is working, etc…

The update process doesn’t lost configuration or passwords !


A little tips working with all of theses ip camera, create some favorites to directly set or unset alarm :

Set alarm to send by ftp and by mail :

Set alarm to send by ftp only  :

Unset alarm :

Don’t forget to change your ip adress/port of course… You can change the “motion_sensitivity=5” to another value according to your environment…

Assistant Professor
UCLouvain, Belgium
+32 479 60 94 63
Reaumur A 027 (Floor 0)
Place Sainte Barbe 2/L5.02.01
1348 Louvain-la-Neuve
Tom Barbette’s brief

Check my research page !

Un·e académique en Sciences de la Communication | SFSIC 2022 – … Assistant Professor
Un·e académique en Sciences de la Communication | SFSIC 2021 – 2022 Post-Doc @ INL
kth-logo.jpg | FEMS - The Federation of European Materials Societies 2018 – 2021 Post-Doc @ KTH
Fichier:University of Liège logo.svg — Wikipédia 2013 – 2018 PhD Student
Past positions

CoNEXT’21-22, HPSR’22, ANCS’21, SIGCOMM’21 Poster session, SIGCOMM’20,22 AEC
ACM/IEEE ToN, Elsevier Computer and Security, IEEE TNSM
GitHub — Wikipédia FastClick ; NPF ; WRK-MP
Community Service