EC
58000
PostgreSQLERRORCriticalSystem ErrorMEDIUM confidence

could not open file

Production Risk

If 58000 occurs when accessing relation files rather than COPY files, it indicates heap or index file loss, which is a data loss event requiring immediate recovery from backup. Check pg_class to map the OID in the error message to a table name.

What this means

Postgres could not open a file needed for a database operation. This includes relation data files, WAL segments, configuration files, or external files referenced by COPY or pg_read_file(). The OS returned an error (ENOENT, EACCES, EMFILE, etc.).

Why it happens
  1. 1A relation file (heap or index) has been deleted or moved outside of Postgres
  2. 2COPY FROM FILENAME referencing a file that does not exist or is not readable by the postgres OS user
  3. 3Too many open file descriptors (EMFILE): max_files_per_process or OS ulimit is too low
  4. 4Permissions on the data directory or a tablespace directory changed
  5. 5A tablespace symlink is broken after a migration or storage reconfiguration
How to reproduce

A COPY command references a server-side file that does not exist.

trigger — this will error
trigger — this will error
COPY users FROM '/tmp/nonexistent_file.csv' CSV HEADER;

expected output

ERROR:  could not open file "/tmp/nonexistent_file.csv" for reading: No such file or directory

Fix 1

Verify the file path and permissions

WHEN When using COPY FROM/TO with a server-side file.

Verify the file path and permissions
-- Check if the file exists and is readable (run as postgres OS user):
-- ls -la /tmp/nonexistent_file.csv

-- Use COPY with stdin for client-side files (avoids server file access):
-- psql -c "\COPY users FROM '/local/path/file.csv' CSV HEADER"
-- (\COPY streams from the client, no server file access needed)

Why this works

COPY FROM with a bare filename opens the file on the server as the postgres OS user. \COPY (the psql meta-command) streams the file from the client over the protocol connection, bypassing server-side file access entirely. \COPY is safer and more portable for client-side files.

Fix 2

Increase the open file descriptor limit

WHEN When EMFILE errors indicate file descriptor exhaustion.

Increase the open file descriptor limit
-- Check current setting:
SHOW max_files_per_process;

-- Increase in postgresql.conf:
-- max_files_per_process = 1000

-- Also increase OS ulimit for the postgres user:
-- ulimit -n 65536 (in the postgres service start script)

SELECT pg_reload_conf();

Why this works

Postgres tracks open file descriptors per backend in the virtual file descriptor (VFD) layer. max_files_per_process limits how many VFDs a single backend opens simultaneously. When this limit is reached Postgres closes and reopens files as needed; if the OS ulimit is too low, open() fails with EMFILE.

What not to do

✕ Run Postgres as root to bypass file permission errors

Running a network service as root is a critical security vulnerability; fix permissions instead.

Sources
Official documentation ↗

src/backend/storage/file/fd.c — FileOpen()

COPY ↗

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