oid2name: command not found

Have You tried accessing the binary with the full path?

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/oid2name - from package: postgresql-contrib

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

On Debian possible default full paths are:

/usr/lib/postgresql/9.4/bin/oid2name - from package: postgresql-contrib-9.4

You may install the required package with command apt-get install {package}
Error in other languages:
oid2name: bevel nie gevind nie
oid2name: comandă negăsită
oid2name: comando não encontrado
oid2name: commande introuvable
oid2name: command not found
oid2name: käsku ei ole
oid2name: không tìm thấy lệnh
oid2name: komanda nerasta
oid2name: Kommando nicht gefunden.
oid2name: kommandot finns inte
oid2name: komut yok
oid2name: nie znaleziono polecenia
oid2name: níor aimsíodh an t-ordú
oid2name: no se encontró la orden
oid2name: no s'ha trobat l'ordre
oid2name: opdracht niet gevonden
oid2name: parancs nem található
oid2name: perintah tidak ditemukan
oid2name: príkaz nenájdený
oid2name: příkaz nenalezen
oid2name: команда не найдена
oid2name: командата не е открита
oid2name: 命令找不到
oid2name: コマンドが見つかりません