notmuch-web: 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/notmuch-web - from package: notmuch-web

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

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