xterm: 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/xterm - from package: xterm

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

On Debian possible default full paths are:

/usr/bin/xterm - from package: xterm

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

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