osmosis --read-pgsql host="localhost" database="X" user="X" password="X" outPipe.0=pg --dd inPipe.0=pg outPipe.0=dd --write-pbf inPipe.0=dd file=myfile.osm.pbf

Jul 22, 2017 9:49:14 AM org.openstreetmap.osmosis.core.Osmosis run
INFO: Osmosis Version 0.44.1
Jul 22, 2017 9:49:15 AM org.openstreetmap.osmosis.core.Osmosis run
INFO: Preparing pipeline.
Jul 22, 2017 9:49:15 AM org.openstreetmap.osmosis.core.Osmosis run
INFO: Launching pipeline execution.
Jul 22, 2017 9:49:15 AM org.openstreetmap.osmosis.core.Osmosis run
INFO: Pipeline executing, waiting for completion.
Jul 22, 2017 9:49:15 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [org/springframework/jdbc/support/sql-error-codes.xml]
Jul 22, 2017 9:49:15 AM org.springframework.jdbc.support.SQLErrorCodesFactory <init>
INFO: SQLErrorCodes loaded: [DB2, Derby, H2, HSQL, Informix, MS-SQL, MySQL, Oracle, PostgreSQL, Sybase]
Jul 22, 2017 9:49:15 AM org.openstreetmap.osmosis.core.pipeline.common.ActiveTaskManager waitForCompletion
SEVERE: Thread for task 1-read-pgsql failed
org.springframework.jdbc.BadSqlGrammarException: StatementCallback; bad SQL grammar [SELECT version FROM schema_info]; nested exception is org.postgresql.util.PSQLException: ERROR: relation "schema_info" does not exist
  Position: 21
        at org.springframework.jdbc.support.SQLErrorCodeSQLExceptionTranslator.doTranslate(SQLErrorCodeSQLExceptionTranslator.java:237)
        at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:72)
        at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:407)
        at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:456)
        at org.springframework.jdbc.core.JdbcTemplate.query(JdbcTemplate.java:464)
        at org.springframework.jdbc.core.JdbcTemplate.queryForObject(JdbcTemplate.java:472)
        at org.springframework.jdbc.core.JdbcTemplate.queryForObject(JdbcTemplate.java:477)
        at org.openstreetmap.osmosis.pgsnapshot.common.SchemaVersionValidator.validateDBVersion(SchemaVersionValidator.java:64)
        at org.openstreetmap.osmosis.pgsnapshot.common.SchemaVersionValidator.validateVersion(SchemaVersionValidator.java:47)
        at org.openstreetmap.osmosis.pgsnapshot.v0_6.impl.PostgreSqlDatasetContext.initialize(PostgreSqlDatasetContext.java:99)
        at org.openstreetmap.osmosis.pgsnapshot.v0_6.impl.PostgreSqlDatasetContext.iterate(PostgreSqlDatasetContext.java:197)
        at org.openstreetmap.osmosis.dataset.v0_6.DumpDataset.process(DumpDataset.java:48)
        at org.openstreetmap.osmosis.pgsnapshot.v0_6.PostgreSqlDatasetReader.run(PostgreSqlDatasetReader.java:53)
        at java.lang.Thread.run(Thread.java:748)
Caused by: org.postgresql.util.PSQLException: ERROR: relation "schema_info" does not exist
  Position: 21
        at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2157)
        at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1886)
        at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:255)
        at org.postgresql.jdbc2.AbstractJdbc2Statement.execute(AbstractJdbc2Statement.java:555)
        at org.postgresql.jdbc2.AbstractJdbc2Statement.executeWithFlags(AbstractJdbc2Statement.java:403)
        at org.postgresql.jdbc2.AbstractJdbc2Statement.executeQuery(AbstractJdbc2Statement.java:283)
        at org.apache.commons.dbcp.DelegatingStatement.executeQuery(DelegatingStatement.java:209)
        at org.apache.commons.dbcp.DelegatingStatement.executeQuery(DelegatingStatement.java:209)
        at org.springframework.jdbc.core.JdbcTemplate$1QueryStatementCallback.doInStatement(JdbcTemplate.java:441)
        at org.springframework.jdbc.core.JdbcTemplate.execute(JdbcTemplate.java:396)
        ... 11 more

Jul 22, 2017 9:49:15 AM org.openstreetmap.osmosis.core.Osmosis main
SEVERE: Execution aborted.
org.openstreetmap.osmosis.core.OsmosisRuntimeException: One or more tasks failed.
        at org.openstreetmap.osmosis.core.pipeline.common.Pipeline.waitForCompletion(Pipeline.java:146)
        at org.openstreetmap.osmosis.core.Osmosis.run(Osmosis.java:92)
        at org.openstreetmap.osmosis.core.Osmosis.main(Osmosis.java:37)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launchStandard(Launcher.java:328)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:238)
        at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:408)
        at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:351)
        at org.codehaus.classworlds.Launcher.main(Launcher.java:31)