Can't create lock file /tmp/.s.PGSQL.5432.lock

Hi all

Running postgres under RedHat9, I moved the /tmp partition to / and copied the /usr into a much larger one in order to
getmore disk space for programs . Hope I did not loose any file. 

One of the problems is that postgre dont start. I Followed the /etc/init.d/postgresql script. It crashes at the line

  su -l postgres -s /bin/sh -c "/usr/bin/pg_ctl  -D $PGDATA -p /usr/bin/postmaster -o '-p ${PGPORT}' start  "


with message

:FATAL:  Can't create lock file /tmp/.s.PGSQL.5432.lock: Permission denied

and the erroneous one

postmaster successfully started

I can understand that the user postgres:postgres cannot write in the /tmp directorythat belong to root:root (as usual),
butit worked before. 
A precision,  I have no .s.PGSQL.5432 file in the /tmp directory.

srwxrwxrwx    1 postgres postgres        0 Dec 11 14:01 ./.s.PGSQL.543


Have any suggestion so that I can rstart the postmaster ?
Should I reinstall postgresql and is it a great risk ?

Cordially

Patrice Durosay