cjb2: 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/cjb2 - from package: djvulibre

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

On Debian possible default full paths are:

/usr/bin/cjb2 - from package: djvulibre-bin

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

Error in other languages:
cjb2: bevel nie gevind nie
cjb2: comandă negăsită
cjb2: comando não encontrado
cjb2: commande introuvable
cjb2: command not found
cjb2: käsku ei ole
cjb2: không tìm thấy lệnh
cjb2: komanda nerasta
cjb2: Kommando nicht gefunden.
cjb2: kommandot finns inte
cjb2: komut yok
cjb2: nie znaleziono polecenia
cjb2: níor aimsíodh an t-ordú
cjb2: no se encontró la orden
cjb2: no s'ha trobat l'ordre
cjb2: opdracht niet gevonden
cjb2: parancs nem található
cjb2: perintah tidak ditemukan
cjb2: príkaz nenájdený
cjb2: příkaz nenalezen
cjb2: команда не найдена
cjb2: командата не е открита
cjb2: 命令找不到
cjb2: コマンドが見つかりません