djvuserve: 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/djvuserve - from package: djvulibre

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

On Debian possible default full paths are:

/usr/bin/djvuserve - from package: djvuserve

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

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