boinc: 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/boinc - from package: boinc-client

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

On Debian possible default full paths are:

/usr/bin/boinc - from package: boinc-client

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

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