barman: 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/barman - from package: barman

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

On Debian possible default full paths are:

/usr/bin/barman - from package: barman

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

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