boincmgr: 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/boincmgr - from package: boinc-manager

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

On Debian possible default full paths are:

/usr/bin/boincmgr - from package: boinc-manager

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

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