Re: BUG #17938: could not open shared memory segment "/PostgreSQL.615216676": No such file or directory

I finally found the source: a broken test in a script that initiates a 
chroot environment. For some reason the author decided to write this:

test -L /dev/shm && rm /dev/shm && mkdir /dev/shm

Instead of re-creating a symlink based /dev/shm as true mountpoint it 
always did so.

Since the issue came up from time to time without any clear relation I 
scanned scripts on the machine that require root permissions – not so 
may to dig through.

This bogus check with immediate action was replaced with a bail out of 
the script in case this would be true. No bug in PostgreSQL.


Am 24.05.23 um 03:09 schrieb Kyotaro Horiguchi:
> At Wed, 24 May 2023 09:57:35 +0900 (JST), Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote in
>> dynamic_shared_memory_type. Outside of Windows, it first prefers
>> posix, then sysv and finally mmap. Thus it is quite usual to use posix
>> for DSM segments. Actually posix is defaultly used for
> 
> It is written in the documentation.
> 
> https://www.postgresql.org/docs/15/runtime-config-resource.html#GUC-DYNAMIC-SHARED-MEMORY-TYPE
> 
>> The use of the mmap option, which is not the default on any
>> platform, is generally discouraged because the operating system may
>> write modified pages back to disk repeatedly, increasing system I/O
>> load; however, it may be useful for debugging, when the pg_dynshmem
>> directory is stored on a RAM disk, or when other shared memory
>> facilities are not available.
> 
> regards.
> 

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