podman-container-tools/podman · error

realloc buffer: %m

Error message

realloc buffer: %m

What it means

While listing a preexec-hooks directory, do_preexec_hooks_dir() grows a buffer one NAME_MAX+1 (256-byte) slot per directory entry with realloc() (pkg/rootless/rootless_linux.c:438). This message means that realloc returned NULL (ENOMEM) and podman exits before the Go runtime starts. The buffer scales linearly with the number of entries in the hooks dir.

Source

Thrown at pkg/rootless/rootless_linux.c:441

  d = opendir (dir);
  if (!d)
    {
      if (errno != ENOENT)
        {
          fprintf (stderr, "opendir %s: %m\n", dir);
          exit (EXIT_FAILURE);
        }
      return;
    }

  errno = 0;

  for (de = readdir (d); de; de = readdir (d))
    {
      buffer = realloc (buffer, (nfiles + 1) * (NAME_MAX + 1));
      if (buffer == NULL)
        {
          fprintf (stderr, "realloc buffer: %m\n");
          exit (EXIT_FAILURE);
        }

      if (de->d_type != DT_REG)
        continue;

      strncpy (buffer + nfiles * (NAME_MAX + 1), de->d_name, NAME_MAX + 1);
      nfiles++;
    }

  qsort (buffer, nfiles, NAME_MAX + 1, (int (*)(const void *, const void *)) strcmp);

  for (i = 0; i < nfiles; i++)
    {
      const char *fname = buffer + i * (NAME_MAX + 1);
      char path[PATH_MAX];
      struct stat st;
      int ret;

View on GitHub (pinned to a2409076ef)

Solutions

1. Count entries in the reported dir ('ls <dir> | wc -l') and remove non-hook files - only regular executables are used
2. Point PODMAN_PREEXEC_HOOKS_DIR at a small dedicated directory containing only the hooks
3. Raise memory limits ('ulimit -v unlimited') or relieve memory pressure and re-run
4. Remove /etc/containers/podman_preexec_hooks.txt if the hooks are not needed

Example fix

# before
export PODMAN_PREEXEC_HOOKS_DIR=/usr/bin   # thousands of entries
podman ps   # realloc buffer: Cannot allocate memory

# after
mkdir -p ~/hooks && cp /path/to/my-hook ~/hooks/
export PODMAN_PREEXEC_HOOKS_DIR=~/hooks
podman ps

# Keep the hooks dir small enough that the realloc buffer is trivial
count=$(ls -1 "${PODMAN_PREEXEC_HOOKS_DIR:-/etc/containers/pre-exec-hooks}" 2>/dev/null | wc -l)
if [ "$count" -gt 1000 ]; then
  echo "too many entries ($count) in preexec hooks dir" >&2
  exit 1
fi

When it happens

Trigger: A preexec-hooks directory containing a very large number of files combined with memory pressure or an RLIMIT_AS/cgroup cap; allocation size is (nfiles+1)*256 bytes.

Common situations: Someone points PODMAN_PREEXEC_HOOKS_DIR at a directory with tens of thousands of files (e.g. a bin dir or a temp dir) instead of a curated hooks dir; low 'ulimit -v'; host near OOM.

Related errors

• malloc: %m
• unable to print to string
• waitpid: %m
• save socket listen environments error: %m
• failed to allocate ps argv

AI-assisted analysis of podman-container-tools/podman@a2409076ef (2026-08-15). Data as JSON: /api/errors/eb18ebcebc7eab04. Report an issue: GitHub.