plot: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/plot - from package: plotutils

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/plot - from package: plotutils

You may install the required package with command apt-get install {package}

Error in other languages:
plot: bevel nie gevind nie
plot: comandă negăsită
plot: comando não encontrado
plot: commande introuvable
plot: command not found
plot: käsku ei ole
plot: không tìm thấy lệnh
plot: komanda nerasta
plot: Kommando nicht gefunden.
plot: kommandot finns inte
plot: komut yok
plot: nie znaleziono polecenia
plot: níor aimsíodh an t-ordú
plot: no se encontró la orden
plot: no s'ha trobat l'ordre
plot: opdracht niet gevonden
plot: parancs nem található
plot: perintah tidak ditemukan
plot: príkaz nenájdený
plot: příkaz nenalezen
plot: команда не найдена
plot: командата не е открита
plot: 命令找不到
plot: コマンドが見つかりません