Financial institutions operating under FINRA 17A-4 regulations face strict requirements for electronic record preservation. The core mandate: data must be written in Write Once Read Many (WORM) format, preventing subsequent modification or deletion - even by system administrators. Traditional solutions like optical media or proprietary hardware (EMC Centera) often prove impractical for modern infrastructure.

While no mainstream Linux filesystem natively provides perfect WORM compliance, several approaches can achieve functional equivalence:

// Example: Setting immutable flag via chattr
chattr +i /archive/transaction_20230515.log

// Verify attribute
lsattr /archive/transaction_20230515.log
----i---------e---- /archive/transaction_20230515.log

Combine filesystem attributes with SELinux policies for defense in depth:

# Create custom SELinux type for WORM files
semanage fcontext -a -t worm_file_t "/archive(/.*)?"
restorecon -Rv /archive

# Policy to prevent even root from modifying worm_file_t
module worm 1.0;

require {
    type unconfined_t;
    type worm_file_t;
    class file { write unlink setattr };
}

deny unconfined_t worm_file_t:file { write unlink setattr };

For stronger guarantees, implement WORM at the block device level:

# Create read-only loop device
dd if=/dev/zero of=worm_store.img bs=1M count=1024
mkfs.ext4 worm_store.img
mount -o loop,ro worm_store.img /mnt/worm

# Cryptographic sealing
openssl enc -aes-256-cbc -salt -in worm_store.img -out worm_store.enc \
    -k "passphrase"

Implement automated integrity checking:

#!/bin/bash
# Generate and verify SHA-256 hashes
find /archive -type f -exec sha256sum {} + > /secure/archive.sha256
sha256sum -c /secure/archive.sha256 | grep -v OK

Consider log-structured filesystems like NILFS2 with custom policies:

# NILFS2 mount options
mount -t nilfs2 -o ro,errors=remount-ro /dev/sdb1 /worm_storage

Financial services firms operating under FINRA 17A-4 face strict requirements for electronic record retention. The regulation mandates that records must be stored on WORM (Write Once, Read Many) media that prevents modification or deletion - even by system administrators. While specialized hardware solutions exist, we can achieve compliance using Linux with careful configuration.

Several approaches can create WORM-like behavior on standard Linux storage:

# Example: Creating an XFS filesystem with unwritable inodes
mkfs.xfs -m crc=1,finobt=1 /dev/sdX1
mount -o ro,nouuid,attr2,inode64 /dev/sdX1 /mnt/worm_store

The chattr +i command provides basic immutability, but we need stronger protections:

# Comprehensive protection script
#!/bin/bash
file="$1"
chmod 444 "$file"
chattr +i "$file"
sha256sum "$file" > "${file}.sha256"
chattr +i "${file}.sha256"

Custom SELinux policies can enforce WORM behavior system-wide:

# SELinux policy module for WORM protection
module worm 1.0;

require {
    type sysadm_t;
    class file { create read write unlink };
}

# Prevent even root from modifying files
neverallow sysadm_t { file_type }:file { write append unlink };

Automating read-only mounts with cryptographic verification:

#!/bin/bash
# Mount and verify script
mount -o remount,ro /mnt/worm_archive
if [ $? -ne 0 ]; then
    logger -t WORM_STORAGE "Failed to remount read-only - alerting"
    exit 1
fi
find /mnt/worm_archive -type f -name "*.sha256" | while read sumfile; do
    if ! sha256sum -c "${sumfile}"; then
        logger -t WORM_STORAGE "Integrity check failed for ${sumfile%%.*}"
    fi
done

Adding LUKS encryption to the WORM storage solution:

# Create encrypted WORM volume
cryptsetup luksFormat --type luks2 /dev/sdX1
cryptsetup open /dev/sdX1 worm_crypt
mkfs.xfs /dev/mapper/worm_crypt
mount -o ro /dev/mapper/worm_crypt /mnt/worm_secure

Automated auditing system to ensure compliance:

#!/bin/bash
# Daily compliance check
if [[ $(findmnt -no OPTIONS /mnt/worm_archive) != *ro* ]]; then
    mail -s "WORM STORAGE COMPLIANCE ALERT" admin@example.com <<< "Writable storage detected"
    exit 1
fi
journalctl -u worm-storage.service --since "1 day ago" | \
    grep -q "remount.*ro" || \
    mail -s "WORM STORAGE MOUNT ALERT" admin@example.com <<< "No daily ro remount detected"