BackupPC_link: 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/share/BackupPC/bin/BackupPC_link - from package: BackupPC

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

On Debian possible default full paths are:

/usr/share/BackupPC/bin/BackupPC_link - from package: BackupPC

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

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