darcs: 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/darcs - from package: darcs

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

On Debian possible default full paths are:

/usr/bin/darcs - from package: darcs

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

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