RE: pg_upgrade -c cannot be run if old cluster is running

Tried (as postgres)
/usr/pgsql-15/bin/pg_upgrade --check -b /usr/pgsql-10/bin/ -B /usr/pgsql-15/bin -d /var/lib/pgsql/10/data -D /mnt/pgdata/pgdirbc15 -p5432 -P5455 -Upostgres -v
Running in verbose mode
Performing Consistency Checks
-----------------------------
Checking cluster versions ok
Current pg_control values:

pg_control version number: 1002
Catalog version number: 201707211
Database system identifier: 6631834114473972710
Latest checkpoint's TimeLineID: 1
Latest checkpoint's full_page_writes: on
Latest checkpoint's NextXID: 0:555
Latest checkpoint's NextOID: 13809
Latest checkpoint's NextMultiXactId: 1
Latest checkpoint's NextMultiOffset: 0
Latest checkpoint's oldestXID: 548
Latest checkpoint's oldestXID's DB: 1
Latest checkpoint's oldestActiveXID: 0
Latest checkpoint's oldestMultiXid: 1
Latest checkpoint's oldestMulti's DB: 1
Latest checkpoint's oldestCommitTsXid:0
Latest checkpoint's newestCommitTsXid:0
Maximum data alignment: 8
Database block size: 8192
Blocks per segment of large relation: 131072
WAL block size: 8192
Bytes per WAL segment: 16777216
Maximum length of identifiers: 64
Maximum columns in an index: 32
Maximum size of a TOAST chunk: 1996
Size of a large-object chunk: 2048
Date/time type storage: 64-bit integers
Float4 argument passing: by value
Float8 argument passing: by value
Data page checksum version: 0

Values to be changed:

First log segment after reset: 000000010000000000000002
Current pg_control values:

pg_control version number: 1300
Catalog version number: 202209061
Database system identifier: 7410372953202657258
Latest checkpoint's TimeLineID: 1
Latest checkpoint's full_page_writes: on
Latest checkpoint's NextXID: 0:732
Latest checkpoint's NextOID: 16387
Latest checkpoint's NextMultiXactId: 1
Latest checkpoint's NextMultiOffset: 0
Latest checkpoint's oldestXID: 716
Latest checkpoint's oldestXID's DB: 1
Latest checkpoint's oldestActiveXID: 0
Latest checkpoint's oldestMultiXid: 1
Latest checkpoint's oldestMulti's DB: 1
Latest checkpoint's oldestCommitTsXid:0
Latest checkpoint's newestCommitTsXid:0
Maximum data alignment: 8
Database block size: 8192
Blocks per segment of large relation: 131072
WAL block size: 8192
Bytes per WAL segment: 16777216
Maximum length of identifiers: 64
Maximum columns in an index: 32
Maximum size of a TOAST chunk: 1996
Size of a large-object chunk: 2048
Date/time type storage: 64-bit integers
Float8 argument passing: by value

Data page checksum version: 0

Values to be changed:

First log segment after reset: 000000010000000000000002
"/usr/pgsql-10/bin/pg_ctl" -w -l "/mnt/pgdata/pgdirbc15/pg_upgrade_output.d/20240905T083735.457/log/pg_upgrade_server.log" -D "/var/lib/pgsql/10/data" -o "-p 5432 -b -c listen_addresses='' -c unix_socket_permissions=0700 -c unix_socket_directories='/var/lib/pgsql'" start >> "/mnt/pgdata/pgdirbc15/pg_upgrade_output.d/20240905T083735.457/log/pg_upgrade_server.log" 2>&1

*failure*
There were problems executing ""/usr/pgsql-10/bin/pg_ctl" -w -l "/mnt/pgdata/pgdirbc15/pg_upgrade_output.d/20240905T083735.457/log/pg_upgrade_server.log" -D "/var/lib/pgsql/10/data" -o "-p 5432 -b -c listen_addresses='' -c unix_socket_permissions=0700 -c unix_socket_directories='/var/lib/pgsql'" start >> "/mnt/pgdata/pgdirbc15/pg_upgrade_output.d/20240905T083735.457/log/pg_upg
rade_server.log" 2>&1"
Consult the last few lines of "/mnt/pgdata/pgdirbc15/pg_upgrade_output.d/20240905T083735.457/log/pg_upgrade_server.log" for the probable cause of the failure.

connection to server on socket "/var/lib/pgsql/.s.PGSQL.5432" failed: No such file or directory
Is the server running locally and accepting connections on that socket?

could not connect to source postmaster started with the command:
"/usr/pgsql-10/bin/pg_ctl" -w -l "/mnt/pgdata/pgdirbc15/pg_upgrade_output.d/20240905T083735.457/log/pg_upgrade_server.log" -D "/var/lib/pgsql/10/data" -o "-p 5432 -b -c listen_addresses=''
-c unix_socket_permissions=0700 -c unix_socket_directories='/var/lib/pgsql'" start
Failure, exiting