rpmmd2solv: 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/rpmmd2solv - from package: libsolv-tools

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

On Debian possible default full paths are:

/usr/bin/rpmmd2solv - from package: libsolv-tools

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

Error in other languages:
rpmmd2solv: bevel nie gevind nie
rpmmd2solv: comandă negăsită
rpmmd2solv: comando não encontrado
rpmmd2solv: commande introuvable
rpmmd2solv: command not found
rpmmd2solv: käsku ei ole
rpmmd2solv: không tìm thấy lệnh
rpmmd2solv: komanda nerasta
rpmmd2solv: Kommando nicht gefunden.
rpmmd2solv: kommandot finns inte
rpmmd2solv: komut yok
rpmmd2solv: nie znaleziono polecenia
rpmmd2solv: níor aimsíodh an t-ordú
rpmmd2solv: no se encontró la orden
rpmmd2solv: no s'ha trobat l'ordre
rpmmd2solv: opdracht niet gevonden
rpmmd2solv: parancs nem található
rpmmd2solv: perintah tidak ditemukan
rpmmd2solv: príkaz nenájdený
rpmmd2solv: příkaz nenalezen
rpmmd2solv: команда не найдена
rpmmd2solv: командата не е открита
rpmmd2solv: 命令找不到
rpmmd2solv: コマンドが見つかりません