pg_dump & pg_restore password using python module subprocess

Question

Problem: Use the PSQL pg_dump and pg_restore in a Python script and using the subprocess module.

Background: I am using the following python 2.7 script from the localhost (i.e. Ubuntu 14.04.5 LTS) to create a backup of a table in a PSQL server (i.e. PostgreSQL 9.4.11) and restore it into the remote host (i.e. Ubuntu 16.04.2 LTS) in a newer version of PSQL server (i.e. PostgreSQL 9.6.2).

#!/usr/bin/python

from subprocess import PIPE,Popen

def dump_table(host_name,database_name,user_name,database_password,table_name):

    command = 'pg_dump -h {0} -d {1} -U {2} -p 5432 -t public.{3} -Fc -f /tmp/table.dmp'\
    .format(host_name,database_name,user_name,table_name)

    p = Popen(command,shell=True,stdin=PIPE)

    return p.communicate('{}\n'.format(database_password))

def restore_table(host_name,database_name,user_name,database_password):

    command = 'pg_restore -h {0} -d {1} -U {2} < /tmp/table.dmp'\
    .format(host_name,database_name,user_name)

    p = Popen(command,shell=True,stdin=PIPE)

    return p.communicate('{}\n'.format(database_password))

def main():
    dump_table('localhost','testdb','user_name','passwd','test_tbl')
    restore_table('remotehost','new_db','user_name','passwd')

if __name__ == "__main__":
    main()

When I use the functions sequentially as above the dump_table() function finishes successfully and creates the /tmp/table.sql file but the restore_table() function returns the following error:

('', 'Password: \npg_restore: [archiver (db)] connection to database "database_name" failed: FATAL: password authentication failed for user "username"\nFATAL: password authentication failed for user "username"\n')*

I have checked the credentials & outputs by executing the commands for pg_restore in the shell and I have also included the credentials to .pgpass (although not relevant since I am passing the password in p.communicate())

Anyone had similar experience? I am pretty much stuck!

Regards, D.

Liston

Answer 1

The following works and the changes made are commented.

I am not sure though why the pg_restore produces that password authentication error when using the full command (i.e. not split in the list) and using shell=True in Popen, but pg_dump on the other hand works fine using shell=True & the full command. Does < have to do anything with it?

#!/usr/bin/python

from subprocess import PIPE,Popen
import shlex

def dump_table(host_name,database_name,user_name,database_password,table_name):

    command = 'pg_dump -h {0} -d {1} -U {2} -p 5432 -t public.{3} -Fc -f /tmp/table.dmp'\
    .format(host_name,database_name,user_name,table_name)

    p = Popen(command,shell=True,stdin=PIPE,stdout=PIPE,stderr=PIPE)

    return p.communicate('{}\n'.format(database_password))

def restore_table(host_name,database_name,user_name,database_password):

    #Remove the '<' from the pg_restore command.
    command = 'pg_restore -h {0} -d {1} -U {2} /tmp/table.dmp'\
              .format(host_name,database_name,user_name)

    #Use shlex to use a list of parameters in Popen instead of using the
    #command as is.
    command = shlex.split(command)

    #Let the shell out of this (i.e. shell=False)
    p = Popen(command,shell=False,stdin=PIPE,stdout=PIPE,stderr=PIPE)

    return p.communicate('{}\n'.format(database_password))

def main():
    dump_table('localhost','testdb','user_name','passwd','test_tbl')
    restore_table('localhost','testdb','user_name','passwd')

if __name__ == "__main__":
    main()

Liston

Answer 2

You can use environment variables https://www.postgresql.org/docs/11/libpq-envars.html and "--no-password" option for pg_dump.

    def dump_schema(host, dbname, user, password, **kwargs):
        command = f'pg_dump --host={host} ' \
            f'--dbname={dbname} ' \
            f'--username={user} ' \
            f'--no-password ' \
            f'--format=c ' \
            f'--file=/tmp/schema.dmp '

        proc = Popen(command, shell=True, env={
            'PGPASSWORD': password
        })
        proc.wait()

Cubicle

I found this page after struggling with (Python 3.7.4) subprocess.run(...) failing to use the input= keyword. Didn't use the shell=True keyword, but the env=did the trick. Some obscur tty related issue. – Weizmann

Answer 3

Here is a python script for taking postgres dump and restore it to a new database.

import subprocess

DB_NAME = 'PrimaryDB'  # your db name

DB_USER = 'postgres' # you db user
DB_HOST = "localhost"
DB_PASSWORD = 'sarath1996'# your db password
dump_success = 1
print ('Backing up %s database ' % (DB_NAME))
command_for_dumping = f'pg_dump --host={DB_HOST} ' \
            f'--dbname={DB_NAME} ' \
            f'--username={DB_USER} ' \
            f'--no-password ' \
            f'--file=backup.dmp '
 try:
     proc = subprocess.Popen(command, shell=True, env={
                   'PGPASSWORD': DB_PASSWORD
                   })
     proc.wait()

 except Exception as e:
        dump_success = 0
        print('Exception happened during dump %s' %(e))


 if dump_success:
    print('db dump successfull')
 print(' restoring to a new database database')

 """database to restore dump must be created with 
the same user as of previous db (in my case user is 'postgres'). 
i have #created a db called ReplicaDB. no need of tables inside. 
restore process will #create tables with data.
"""

backup_file = '/home/Downloads/BlogTemplate/BlogTemplate/backup.dmp' 
"""give absolute path of your dump file. This script will create the backup.dmp in the same directory from which u are running the script """



if not dump_success:
    print('dump unsucessfull. retsore not possible')
 else:
    try:
        process = subprocess.Popen(
                        ['pg_restore',
                         '--no-owner',
                         '--dbname=postgresql://{}:{}@{}:{}/{}'.format('postgres',#db user
                                                                       'sarath1996', #db password
                                                                       'localhost',  #db host
                                                                       '5432', 'ReplicaDB'), #db port ,#db name
                         '-v',
                         backup_file],
                        stdout=subprocess.PIPE
                    )
        output = process.communicate()[0]

     except Exception as e:
           print('Exception during restore %e' %(e) )

Wooldridge

just to note here, you must provide --format=custom in the command_for_dumping in order to work with pg_restore. – Bantamweight

Answer 4

You can try using the dbname option like this:

def backup():
    command = 'pg_dump --dbname=postgresql://{}:{}@{}:{}/{} > {}/schema.dmp'.format(DB_USER, DB_PASS, DB_HOST, DB_PORT, DB_NAME, BACKUP_DIR)
    try:
        proc = subprocess.Popen(command, shell=True, env={
            'PGPASSWORD': DB_PASS
        })
        proc.wait()
        print('Backup successful')
    except Exception as e:
        print('Exception happened during backup: %s' % (e))

Note: This also works for backing up postgres Airflow in a Docker container

Sorel