byobu-select-session: 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/byobu-select-session - from package: byobu

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

On Debian possible default full paths are:

/usr/bin/byobu-select-session - from package: byobu

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

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