MuntashirAkon/AppManager · error · BackupException

Could not cache

Error message

Could not cache 

What it means

Before backing up KeyStore files, backupKeyStore() copies each keystore file into a cache directory under a placeholder-based name. If copying a particular file fails, this BackupException naming the file is thrown with the cause attached.

Source

Thrown at app/src/main/java/io/github/muntashirakon/AppManager/backup/BackupOp.java:421

            Path masterKeyFile = KeyStoreUtils.getMasterKey(mUserId);
            // Master key exists, so take its checksum to verify it during the restore
            mChecksum.add(MASTER_KEY, DigestUtils.getHexDigest(mMetadata.info.checksumAlgo,
                    masterKeyFile.getContentAsString().getBytes()));
        } catch (FileNotFoundException ignore) {
        }
        // Store the KeyStore files
        Path cachePath = Paths.get(FileUtils.getCachePath());
        List<String> cachedKeyStoreFileNames = new ArrayList<>();
        List<String> keyStoreFilters = new ArrayList<>();
        for (String keyStoreFileName : KeyStoreUtils.getKeyStoreFiles(mApplicationInfo.uid, mUserId)) {
            try {
                String newFileName = Utils.replaceOnce(keyStoreFileName, String.valueOf(mApplicationInfo.uid),
                        String.valueOf(KEYSTORE_PLACEHOLDER));
                IoUtils.copy(keyStorePath.findFile(keyStoreFileName), cachePath.findOrCreateFile(newFileName, null));
                cachedKeyStoreFileNames.add(newFileName);
                keyStoreFilters.add(Pattern.quote(newFileName));
            } catch (Throwable e) {
                throw new BackupException("Could not cache " + keyStoreFileName, e);
            }
        }
        if (cachedKeyStoreFileNames.isEmpty()) {
            throw new BackupException("There were some KeyStore items but they couldn't be cached before taking a backup.");
        }
        String keyStorePrefix = KEYSTORE_PREFIX + getExt(mMetadata.info.tarType);
        Path[] backedUpKeyStoreFiles;
        try {
            backedUpKeyStoreFiles = TarUtils.create(mMetadata.info.tarType, cachePath, mBackupItem.getUnencryptedBackupPath(), keyStorePrefix,
                            keyStoreFilters.toArray(new String[0]), null, null, false)
                    .toArray(new Path[0]);
        } catch (Throwable th) {
            throw new BackupException("Could not backup KeyStore item.", th);
        }
        // Remove cache
        for (String name : cachedKeyStoreFileNames) {
            try {
                cachePath.findFile(name).delete();

View on GitHub (pinned to 0152f468fc)

Solutions

1. Check the cause to see if it is a read error (source) or write error (cache)
2. Confirm the keystore source file still exists before copying
3. Free space in the cache directory
4. Ensure the keystore filename contains the expected uid for KEYSTORE_PLACEHOLDER replacement

Example fix

// before
IoUtils.copy(keyStorePath.findFile(keyStoreFileName), cachePath.findOrCreateFile(newFileName, null));
// after
VirtualFile src = keyStorePath.findFile(keyStoreFileName);
if (src == null) { Log.w(TAG, "Skipping missing keystore file " + keyStoreFileName); continue; }
IoUtils.copy(src, cachePath.findOrCreateFile(newFileName, null));

if (keyStorePath.findFile(keyStoreFileName) == null) {
    Log.w(TAG, "keystore file missing: " + keyStoreFileName);
    return; // skip
}
if (cachePath.getFreeSpace() < keyStorePath.findFile(keyStoreFileName).getSize()) { /* free space */ }

static boolean canCache(VirtualFile src, VirtualPath cacheDir) {
    return src != null && src.exists() && cacheDir != null && cacheDir.canWrite();
}

try {
    IoUtils.copy(src, dst);
} catch (Throwable e) {
    throw new BackupException("Could not cache " + name, e);
}

When it happens

Trigger: IoUtils.copy(keyStorePath.findFile(keyStoreFileName), cachePath.findOrCreateFile(...)) throws for a specific keystore file — source missing or cache file cannot be created/written.

Common situations: Keystore path listing changed between listing and copy; cache partition full; filename no longer contains the uid so replaceOnce produced an unexpected name; permission issues in /data/misc/keystore.

Understand the failure class

Background: "failed to write file", "Could not save figure", "Error saving remote file" — file write failed: causes and fixes across languages and libraries — this error's family across 38 libraries.

Related errors

• Could not backup KeyStore item.
• Could not cache APK file
• Could not cache the APK file
• Could not get backup files.
• Could not retrieve metadata from backup.

AI-assisted analysis of MuntashirAkon/AppManager@0152f468fc (2026-09-12). Data as JSON: /api/errors/3191a0e5b383d3fc. Report an issue: GitHub.