Postgres won't start

Linux Mint (from Ubuntu) version 9.1.

Postgres will no longer start, but I cannot find out why.

Command line:
$ /usr/lib/postgresql/9.1/bin/pg_ctl start -D /home/postgresql/9.1/main -l
/var/log/postgresql/postgresql-9.1-main.log -s -w -o '-c
config_file="/etc/postgresql/9.1/main/postgresql.conf"'
pg_ctl: could not start server
Examine the log output.

There is no error message in the log:
2013-08-08 21:35:33 GMT DEBUG: postgres: PostmasterMain: initial
environment dump:
2013-08-08 21:35:33 GMT DEBUG: -----------------------------------------
2013-08-08 21:35:33 GMT DEBUG: MAIL=/var/mail/postgres
2013-08-08 21:35:33 GMT DEBUG: USER=postgres
2013-08-08 21:35:33 GMT DEBUG: LANGUAGE=en_GB:en
2013-08-08 21:35:33 GMT DEBUG: LC_TIME=C
2013-08-08 21:35:33 GMT DEBUG: SHLVL=1
2013-08-08 21:35:33 GMT DEBUG: HOME=/var/lib/postgresql
2013-08-08 21:35:33 GMT DEBUG:
XDG_SESSION_COOKIE=4464da00797efbf61ba9be4b517969c3-1375997124.817437-835692463
2013-08-08 21:35:33 GMT DEBUG: LC_MONETARY=C
2013-08-08 21:35:33 GMT DEBUG: COLORTERM=mate-terminal
2013-08-08 21:35:33 GMT DEBUG: PG_GRANDPARENT_PID=15848
2013-08-08 21:35:33 GMT DEBUG: LOGNAME=postgres
2013-08-08 21:35:33 GMT DEBUG: _=/usr/lib/postgresql/9.1/bin/pg_ctl
2013-08-08 21:35:33 GMT DEBUG: TERM=xterm
2013-08-08 21:35:33 GMT DEBUG: PGLOCALEDIR=/usr/share/locale
2013-08-08 21:35:33 GMT DEBUG: PGSYSCONFDIR=/etc/postgresql-common
2013-08-08 21:35:33 GMT DEBUG:
PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
2013-08-08 21:35:33 GMT DEBUG: LC_ADDRESS=en_GB.UTF-8
2013-08-08 21:35:33 GMT DEBUG: XDG_RUNTIME_DIR=/run/user/postgres
2013-08-08 21:35:33 GMT DEBUG: DISPLAY=:0
2013-08-08 21:35:33 GMT DEBUG: LC_TELEPHONE=en_GB.UTF-8
2013-08-08 21:35:33 GMT DEBUG: LANG=en_GB.UTF-8
2013-08-08 21:35:33 GMT DEBUG: XAUTHORITY=/home/olly/.Xauthority
2013-08-08 21:35:33 GMT DEBUG: SHELL=/bin/bash
2013-08-08 21:35:33 GMT DEBUG: LC_NAME=en_GB.UTF-8
2013-08-08 21:35:33 GMT DEBUG: LC_MEASUREMENT=en_GB.UTF-8
2013-08-08 21:35:33 GMT DEBUG: LC_IDENTIFICATION=en_GB.UTF-8
2013-08-08 21:35:33 GMT DEBUG: PWD=/var/lib/postgresql
2013-08-08 21:35:33 GMT DEBUG: LC_NUMERIC=C
2013-08-08 21:35:33 GMT DEBUG: LC_PAPER=en_GB.UTF-8
2013-08-08 21:35:33 GMT DEBUG: PGDATA=/home/postgresql/9.1/main
2013-08-08 21:35:33 GMT DEBUG: LC_COLLATE=en_GB.UTF-8
2013-08-08 21:35:33 GMT DEBUG: LC_CTYPE=en_GB.UTF-8
2013-08-08 21:35:33 GMT DEBUG: LC_MESSAGES=en_GB.UTF-8
2013-08-08 21:35:33 GMT DEBUG: -----------------------------------------
2013-08-08 21:35:33 GMT DEBUG: TZ "localtime" gets max score 5200
2013-08-08 21:35:33 GMT DEBUG: TZ "Singapore" scores 0: at 1357776000
2013-01-10 08:00:00 std versus 2013-01-10 01:00:00 std
2013-08-08 21:35:33 GMT DEBUG: TZ "GMT" scores 0: at 1357776000 2013-01-10
00:00:00 std versus 2013-01-10 01:00:00 std
...[many lines of timezone info deleted]...
2013-08-08 21:35:34 GMT DEBUG: TZ "Atlantic/St_Helena" scores 0: at
1357776000 2013-01-10 00:00:00 std versus 2013-01-10 01:00:00 std
2013-08-08 23:35:34 CEST DEBUG: invoking IpcMemoryCreate(size=32399360)
2013-08-08 23:35:34 CEST DEBUG: removing file "pg_notify/0000"
2013-08-08 23:35:34 CEST DEBUG: max_safe_fds = 985, usable_fds = 1000,
already_open = 5
2013-08-08 23:35:34 CEST DEBUG: logger shutting down
2013-08-08 23:35:34 CEST DEBUG: shmem_exit(0): 0 callbacks to make
2013-08-08 23:35:34 CEST DEBUG: proc_exit(0): 0 callbacks to make
2013-08-08 23:35:34 CEST DEBUG: exit(0)
2013-08-08 23:35:34 CEST DEBUG: shmem_exit(-1): 0 callbacks to make
2013-08-08 23:35:34 CEST DEBUG: proc_exit(-1): 0 callbacks to make

# cat /proc/sys/kernel/shmmax
33554432

I increased this to 64Mb
# cat /proc/sys/kernel/shmmax
67108864

but it made no difference