Not 100% sure if this is a bug fix or an improvement. I wrote the NEWS
entry as a bug fix because the behavior seems unintentional and I am
leaning towards that.
'shred' does not work on FIFOs since the data is never written to
disk; their directory entry just serves as a means to access the pipe.
With that in mind, the current behavior seems poor, in my opinion:
$ timeout --verbose 10 shred fifo
timeout: sending signal TERM to command ‘shred’
However, if you open a reader:
$ cat fifo > /dev/null &
[1] 1032724
$ shred fifo
shred: fifo: invalid file type
[1]+ Done cat fifo > /dev/null
This patch changes the behavior to open with O_NONBLOCK, similar to
what is done in 'sync':
$ ./src/shred fifo
shred: fifo: invalid file type
-- 8< --
* NEWS: Mention the bug fix.
* src/shred.c (wipefile): Open the file with O_NONBLOCK.
* tests/shred/fifo.sh: New file.
* tests/local.mk (all_tests): Add the new test.
---
NEWS | 3 +++
src/shred.c | 26 +++++++++++++++++++-------
tests/local.mk | 1 +
tests/shred/fifo.sh | 43 +++++++++++++++++++++++++++++++++++++++++++
4 files changed, 66 insertions(+), 7 deletions(-)
create mode 100755 tests/shred/fifo.sh
diff --git a/NEWS b/NEWS
index a105c4884..f8c43d5ed 100644
--- a/NEWS
+++ b/NEWS
@@ -12,6 +12,9 @@ GNU coreutils NEWS -*-
outline -*-
standard output is fully buffered, e.g., when redirected to a file.
[bug introduced in coreutils-9.10]
+ 'shred' no longer blocks when opening a FIFO that has no readers.
+ [This bug was present in "the beginning".]
+
'unexpand -t' no longer overflows a heap buffer, for tab values >
SIZE_MAX/16.
[bug introduced in coreutils-9.11]
diff --git a/src/shred.c b/src/shred.c
index b5bf6f3f0..316268691 100644
--- a/src/shred.c
+++ b/src/shred.c
@@ -1139,21 +1139,33 @@ static bool
wipefile (char *name, char const *qname,
struct randint_source *s, struct Options const *flags)
{
- bool ok;
- int fd;
-
- fd = open (name, O_WRONLY | O_NOCTTY | O_BINARY);
+ int fd = open (name, O_WRONLY | O_NOCTTY | O_NONBLOCK | O_BINARY);
if (fd < 0
&& (errno == EACCES && flags->force)
&& chmod (name, S_IWUSR) == 0)
- fd = open (name, O_WRONLY | O_NOCTTY | O_BINARY);
+ fd = open (name, O_WRONLY | O_NOCTTY | O_NONBLOCK | O_BINARY);
if (fd < 0)
{
- error (0, errno, _("%s: failed to open for writing"), qname);
+ struct stat st;
+
+ /* Try to give a more meaningful error message if we attempt to
+ open a FIFO with no readers. */
+ if (errno == ENXIO && 0 <= stat (name, &st) && S_ISFIFO (st.st_mode))
+ error (0, 0, _("%s: invalid file type"), qname);
+ else
+ error (0, errno, _("%s: failed to open for writing"), qname);
return false;
}
- ok = do_wipefd (fd, qname, s, flags);
+ /* We used O_NONBLOCK to prevent blocking when opening a FIFO.
+ Reset that here. */
+ int fd_flags = fcntl (fd, F_GETFL);
+ bool ok = 0 <= fd_flags && 0 <= fcntl (fd, F_SETFL, fd_flags & ~O_NONBLOCK);
+ if (ok)
+ ok = do_wipefd (fd, qname, s, flags);
+ else
+ error (0, errno, _("couldn't reset non-blocking mode %s"), qname);
+
if (close (fd) != 0)
{
error (0, errno, _("%s: failed to close"), qname);
diff --git a/tests/local.mk b/tests/local.mk
index 727cf8b58..fd96d7f3a 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -418,6 +418,7 @@ all_tests = \
tests/cksum/sha384sum.pl \
tests/cksum/sha512sum.pl \
tests/cksum/cksum-sha3.sh \
+ tests/shred/fifo.sh \
tests/shred/shred-exact.sh \
tests/shred/shred-passes.sh \
tests/shred/shred-remove.sh \
diff --git a/tests/shred/fifo.sh b/tests/shred/fifo.sh
new file mode 100755
index 000000000..746466b60
--- /dev/null
+++ b/tests/shred/fifo.sh
@@ -0,0 +1,43 @@
+#!/bin/sh
+# Test that 'shred' behaves correctly on FIFOs.
+
+# Copyright (C) 2026 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ shred
+
+mkfifo_or_skip_ fifo
+
+# Test 'shred' on a FIFO with no readers.
+cat <<\EOF >exp || framework_failure_
+shred: fifo: invalid file type
+EOF
+returns_ 1 timeout 10 shred fifo >out 2>err || fail=1
+compare /dev/null out || fail=1
+compare exp err || fail=1
+
+# Terminate any background processes.
+cleanup_() { kill $pid 2>/dev/null && wait $pid; }
+
+# Test 'shred' on a FIFO with a reader. After the file descriptor is
+# opened, 'cat' will be unblocked.
+timeout 10 cat pipe > copy & pid=$!
+returns_ 1 timeout 10 shred fifo >out 2>err || fail=1
+compare /dev/null out || fail=1
+compare exp err || fail=1
+kill -0 $pid && fail=1
+
+Exit $fail
--
2.54.0
