dzen2: 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/dzen2 - from package: dzen2

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

On Debian possible default full paths are:

/usr/bin/dzen2 - from package: dzen2

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

Error in other languages:
dzen2: bevel nie gevind nie
dzen2: comandă negăsită
dzen2: comando não encontrado
dzen2: commande introuvable
dzen2: command not found
dzen2: käsku ei ole
dzen2: không tìm thấy lệnh
dzen2: komanda nerasta
dzen2: Kommando nicht gefunden.
dzen2: kommandot finns inte
dzen2: komut yok
dzen2: nie znaleziono polecenia
dzen2: níor aimsíodh an t-ordú
dzen2: no se encontró la orden
dzen2: no s'ha trobat l'ordre
dzen2: opdracht niet gevonden
dzen2: parancs nem található
dzen2: perintah tidak ditemukan
dzen2: príkaz nenájdený
dzen2: příkaz nenalezen
dzen2: команда не найдена
dzen2: командата не е открита
dzen2: 命令找不到
dzen2: コマンドが見つかりません