pg_dumpall: 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/pg_dumpall - from package: postgresql

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

On Debian possible default full paths are:

/usr/bin/pg_dumpall - from package: postgresql-client-common
/usr/lib/postgresql/9.4/bin/pg_dumpall - from package: postgresql-client-9.4

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

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