clear: 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/clear - from package: ncurses

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

On Debian possible default full paths are:

/usr/bin/clear - from package: ncurses-bin

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

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