coqdep: 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 Debian possible default full paths are:

/usr/bin/coqdep - from package: coq

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

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