diff --git a/lucene/core/src/java/org/apache/lucene/store/Directory.java b/lucene/core/src/java/org/apache/lucene/store/Directory.java
index f25113c4a79..369e6f45473 100644
--- a/lucene/core/src/java/org/apache/lucene/store/Directory.java
+++ b/lucene/core/src/java/org/apache/lucene/store/Directory.java
@@ -172,12 +172,12 @@ public abstract class Directory implements Closeable {
 
   /**
    * Copies an existing {@code src} file from directory {@code from} to a non-existent file {@code
-   * dest} in this directory.
+   * dest} in this directory. The given IOContext is only used for opening the destination file.
    */
   public void copyFrom(Directory from, String src, String dest, IOContext context)
       throws IOException {
     boolean success = false;
-    try (IndexInput is = from.openInput(src, context);
+    try (IndexInput is = from.openInput(src, IOContext.READONCE);
         IndexOutput os = createOutput(dest, context)) {
       os.copyBytes(is, is.length());
       success = true;
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestAllFilesCheckIndexHeader.java b/lucene/core/src/test/org/apache/lucene/index/TestAllFilesCheckIndexHeader.java
index 0fe1465fd0c..f826ee45b66 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestAllFilesCheckIndexHeader.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestAllFilesCheckIndexHeader.java
@@ -115,7 +115,7 @@ public class TestAllFilesCheckIndexHeader extends LuceneTestCase {
           // time this will only require one iteration!
           while (true) {
             try (IndexOutput out = dirCopy.createOutput(name, IOContext.DEFAULT);
-                IndexInput in = dir.openInput(name, IOContext.DEFAULT)) {
+                IndexInput in = dir.openInput(name, IOContext.READONCE)) {
               // keeps same file length, but replaces the first wrongBytes with random bytes:
               byte[] bytes = new byte[wrongBytes];
               random().nextBytes(bytes);
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestAllFilesDetectMismatchedChecksum.java b/lucene/core/src/test/org/apache/lucene/index/TestAllFilesDetectMismatchedChecksum.java
index ef0fca81aeb..0022a5e3cae 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestAllFilesDetectMismatchedChecksum.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestAllFilesDetectMismatchedChecksum.java
@@ -122,7 +122,7 @@ public class TestAllFilesDetectMismatchedChecksum extends LuceneTestCase {
           dirCopy.copyFrom(dir, name, name, IOContext.DEFAULT);
         } else {
           try (IndexOutput out = dirCopy.createOutput(name, IOContext.DEFAULT);
-              IndexInput in = dir.openInput(name, IOContext.DEFAULT)) {
+              IndexInput in = dir.openInput(name, IOContext.READONCE)) {
             out.copyBytes(in, flipOffset);
             out.writeByte((byte) (in.readByte() + TestUtil.nextInt(random(), 0x01, 0xFF)));
             out.copyBytes(in, victimLength - flipOffset - 1);
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestAllFilesDetectTruncation.java b/lucene/core/src/test/org/apache/lucene/index/TestAllFilesDetectTruncation.java
index 6b4abc87a09..b72fa0f2980 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestAllFilesDetectTruncation.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestAllFilesDetectTruncation.java
@@ -152,7 +152,7 @@ public class TestAllFilesDetectTruncation extends LuceneTestCase {
           }
 
           try (IndexOutput out = dirCopy.createOutput(name, IOContext.DEFAULT);
-              IndexInput in = dir.openInput(name, IOContext.DEFAULT)) {
+              IndexInput in = dir.openInput(name, IOContext.READONCE)) {
             out.copyBytes(in, victimLength - lostBytes);
           }
         }
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestAllFilesHaveChecksumFooter.java b/lucene/core/src/test/org/apache/lucene/index/TestAllFilesHaveChecksumFooter.java
index b9dd3656da4..3826962779a 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestAllFilesHaveChecksumFooter.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestAllFilesHaveChecksumFooter.java
@@ -19,6 +19,7 @@ package org.apache.lucene.index;
 import java.io.IOException;
 import org.apache.lucene.codecs.CodecUtil;
 import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.IOContext;
 import org.apache.lucene.store.IndexInput;
 import org.apache.lucene.tests.analysis.MockAnalyzer;
 import org.apache.lucene.tests.index.RandomIndexWriter;
@@ -77,7 +78,7 @@ public class TestAllFilesHaveChecksumFooter extends LuceneTestCase {
   }
 
   private void checkFooter(Directory dir, String file) throws IOException {
-    try (IndexInput in = dir.openInput(file, newIOContext(random()))) {
+    try (IndexInput in = dir.openInput(file, IOContext.READONCE)) {
       CodecUtil.checksumEntireFile(in);
     }
   }
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestAllFilesHaveCodecHeader.java b/lucene/core/src/test/org/apache/lucene/index/TestAllFilesHaveCodecHeader.java
index cced891b86e..76c3ee75f25 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestAllFilesHaveCodecHeader.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestAllFilesHaveCodecHeader.java
@@ -21,6 +21,7 @@ import java.util.HashMap;
 import java.util.Map;
 import org.apache.lucene.codecs.CodecUtil;
 import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.IOContext;
 import org.apache.lucene.store.IndexInput;
 import org.apache.lucene.tests.analysis.MockAnalyzer;
 import org.apache.lucene.tests.index.RandomIndexWriter;
@@ -84,7 +85,7 @@ public class TestAllFilesHaveCodecHeader extends LuceneTestCase {
   private void checkHeader(
       Directory dir, String file, Map<String, String> namesToExtensions, byte[] id)
       throws IOException {
-    try (IndexInput in = dir.openInput(file, newIOContext(random()))) {
+    try (IndexInput in = dir.openInput(file, IOContext.READONCE)) {
       int val = CodecUtil.readBEInt(in);
       assertEquals(
           file + " has no codec header, instead found: " + val, CodecUtil.CODEC_MAGIC, val);
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestIndexWriterExceptions.java b/lucene/core/src/test/org/apache/lucene/index/TestIndexWriterExceptions.java
index 674ba6eac65..0e7f7814f92 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestIndexWriterExceptions.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestIndexWriterExceptions.java
@@ -1275,7 +1275,7 @@ public class TestIndexWriterExceptions extends LuceneTestCase {
     assertTrue("segment generation should be > 0 but got " + gen, gen > 0);
 
     final String segmentsFileName = SegmentInfos.getLastCommitSegmentsFileName(dir);
-    IndexInput in = dir.openInput(segmentsFileName, newIOContext(random()));
+    IndexInput in = dir.openInput(segmentsFileName, IOContext.READONCE);
     IndexOutput out =
         dir.createOutput(
             IndexFileNames.fileNameFromGeneration(IndexFileNames.SEGMENTS, "", 1 + gen),
@@ -1320,7 +1320,7 @@ public class TestIndexWriterExceptions extends LuceneTestCase {
     String fileNameIn = SegmentInfos.getLastCommitSegmentsFileName(dir);
     String fileNameOut =
         IndexFileNames.fileNameFromGeneration(IndexFileNames.SEGMENTS, "", 1 + gen);
-    IndexInput in = dir.openInput(fileNameIn, newIOContext(random()));
+    IndexInput in = dir.openInput(fileNameIn, IOContext.READONCE);
     IndexOutput out = dir.createOutput(fileNameOut, newIOContext(random()));
     long length = in.length();
     for (int i = 0; i < length - 1; i++) {
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestSegmentInfos.java b/lucene/core/src/test/org/apache/lucene/index/TestSegmentInfos.java
index a4521649b89..90b0a07aa34 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestSegmentInfos.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestSegmentInfos.java
@@ -367,7 +367,7 @@ public class TestSegmentInfos extends LuceneTestCase {
     boolean corrupt = false;
     for (String file : dir.listAll()) {
       if (file.startsWith(IndexFileNames.SEGMENTS)) {
-        try (IndexInput in = dir.openInput(file, IOContext.DEFAULT);
+        try (IndexInput in = dir.openInput(file, IOContext.READONCE);
             IndexOutput out = corruptDir.createOutput(file, IOContext.DEFAULT)) {
           final long corruptIndex = TestUtil.nextLong(random(), 0, in.length() - 1);
           out.copyBytes(in, corruptIndex);
@@ -375,7 +375,7 @@ public class TestSegmentInfos extends LuceneTestCase {
           out.writeByte((byte) b);
           out.copyBytes(in, in.length() - in.getFilePointer());
         }
-        try (IndexInput in = corruptDir.openInput(file, IOContext.DEFAULT)) {
+        try (IndexInput in = corruptDir.openInput(file, IOContext.READONCE)) {
           CodecUtil.checksumEntireFile(in);
           if (VERBOSE) {
             System.out.println("TEST: Altering the file did not update the checksum, aborting...");
diff --git a/lucene/core/src/test/org/apache/lucene/index/TestSnapshotDeletionPolicy.java b/lucene/core/src/test/org/apache/lucene/index/TestSnapshotDeletionPolicy.java
index a341a10349b..0a35e17084c 100644
--- a/lucene/core/src/test/org/apache/lucene/index/TestSnapshotDeletionPolicy.java
+++ b/lucene/core/src/test/org/apache/lucene/index/TestSnapshotDeletionPolicy.java
@@ -26,6 +26,7 @@ import org.apache.lucene.document.Document;
 import org.apache.lucene.document.FieldType;
 import org.apache.lucene.document.TextField;
 import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.IOContext;
 import org.apache.lucene.store.IndexInput;
 import org.apache.lucene.tests.analysis.MockAnalyzer;
 import org.apache.lucene.tests.util.LuceneTestCase;
@@ -230,7 +231,7 @@ public class TestSnapshotDeletionPolicy extends LuceneTestCase {
 
   @SuppressForbidden(reason = "Thread sleep")
   private void readFile(Directory dir, String name) throws Exception {
-    IndexInput input = dir.openInput(name, newIOContext(random()));
+    IndexInput input = dir.openInput(name, IOContext.READONCE);
     try {
       long size = dir.fileLength(name);
       long bytesLeft = size;
diff --git a/lucene/luke/src/java/org/apache/lucene/luke/models/util/IndexUtils.java b/lucene/luke/src/java/org/apache/lucene/luke/models/util/IndexUtils.java
index 735fc6db818..9357a467487 100644
--- a/lucene/luke/src/java/org/apache/lucene/luke/models/util/IndexUtils.java
+++ b/lucene/luke/src/java/org/apache/lucene/luke/models/util/IndexUtils.java
@@ -341,7 +341,7 @@ public final class IndexUtils {
       @Override
       protected String doBody(String segmentFileName) throws IOException {
         String format = "unknown";
-        try (IndexInput in = dir.openInput(segmentFileName, IOContext.DEFAULT)) {
+        try (IndexInput in = dir.openInput(segmentFileName, IOContext.READONCE)) {
           if (CodecUtil.CODEC_MAGIC == CodecUtil.readBEInt(in)) {
             int actualVersion =
                 CodecUtil.checkHeaderNoMagic(
diff --git a/lucene/test-framework/src/java/org/apache/lucene/tests/store/MockDirectoryWrapper.java b/lucene/test-framework/src/java/org/apache/lucene/tests/store/MockDirectoryWrapper.java
index 2589d082fc9..2f30a8cda50 100644
--- a/lucene/test-framework/src/java/org/apache/lucene/tests/store/MockDirectoryWrapper.java
+++ b/lucene/test-framework/src/java/org/apache/lucene/tests/store/MockDirectoryWrapper.java
@@ -814,6 +814,14 @@ public class MockDirectoryWrapper extends BaseDirectoryWrapper {
 
     context = LuceneTestCase.newIOContext(randomState, context);
     final boolean confined = context == IOContext.READONCE;
+    if (name.startsWith(IndexFileNames.SEGMENTS) && confined == false) {
+      throw new RuntimeException(
+          "MockDirectoryWrapper: opening segments file ["
+              + name
+              + "] with a non-READONCE context["
+              + context
+              + "]");
+    }
     IndexInput delegateInput = in.openInput(name, context);
 
     final IndexInput ii;
diff --git a/lucene/test-framework/src/java/org/apache/lucene/tests/util/LuceneTestCase.java b/lucene/test-framework/src/java/org/apache/lucene/tests/util/LuceneTestCase.java
index c61968d557e..91942f660f9 100644
--- a/lucene/test-framework/src/java/org/apache/lucene/tests/util/LuceneTestCase.java
+++ b/lucene/test-framework/src/java/org/apache/lucene/tests/util/LuceneTestCase.java
@@ -2989,7 +2989,7 @@ public abstract class LuceneTestCase extends Assert {
    */
   public static boolean slowFileExists(Directory dir, String fileName) throws IOException {
     try {
-      dir.openInput(fileName, IOContext.DEFAULT).close();
+      dir.openInput(fileName, IOContext.READONCE).close();
       return true;
     } catch (@SuppressWarnings("unused") NoSuchFileException | FileNotFoundException e) {
       return false;