FAPOLICYD.CONF:(5)

NAME
fapolicyd.conf - fapolicyd configuration file

DESCRIPTION
The file /etc/fapolicyd/fapolicyd.conf contains configuration information for the application whitelisting daemon configuration. This file allows the admin to tune the performance and actions of the fapolicyd during runtime. This file contains one configuration keyword per line, an equal sign, and then followed by appropriate configuration information. All option names and values are case insensitive. The keywords recognized are listed and described below. Each line should be limited to 160 characters or the line will be skipped. You may add comments to the file by starting the line with a '#' character.

permissive
    This option is either a 0 to mean send policy decisions to the kernel for enforcement. Or it can be a 1 to mean always allow the access even if policy would block it. This should only be used for policy testing and debug. The default value is 0.

nice_val
    This option gives fapolicyd a scheduler boost. The number can be from 0 to 20. The default value is 10.

q_size
    This option is used to control how big of an internal queue that fapolicyd will use. If requests come in faster than fapolicyd can answer, the queue holds the pending requests. If the do_stat_report is enabled, when fapolicyd shutsdown it will provide some statistics which includes maximum queue depth used. This information can be used to help tune performance. The default value is 800. Also note, this value means that fapolicyd gets a file descriptor for that entry. There is an rlimit cap controlled by systemd's LimitNOFILE setting for the service. You may also need to adjust it if the q_size exceeds its value. When decision_threads is greater than 1, this value is applied to each decision worker. The total userspace queue capacity and approximate fanotify permission file descriptor budget are therefore decision_threads multiplied by q_size, plus the daemon's other descriptors.

decision_threads
    This option controls how many decision worker threads fapolicyd is configured to use. The default value is 1. The value must be at least 1, no larger than the number of online CPU cores, and no larger than the daemon's supported maximum. Startup validation also checks that the configured worker count fits the LMDB reader-slot reservation, estimated fixed worker memory budget, and file descriptor budget implied by q_size. Each decision worker owns its own event queue, subject cache, object cache, and subject-slot defer array. Increasing this value can reduce queueing when decision processing is CPU-bound, but it also increases the fixed memory and file descriptor footprint of those per-worker resources. The trust database map is shared, but each worker still needs an LMDB reader slot. This setting is applied when the daemon starts; restart fapolicyd after changing it.

uid This can be a number or an account name which fapolicyd should switch to during startup. The default value is 0 because it is guaranteed to exist. But it is recommended to use the fapolicyd account if that exists.

gid This can be a number or an group name which fapolicyd should switch to during startup. The default value is 0 because it is guaranteed to exist. But it is recommended to use the fapolicyd group if that exists.

do_stat_report
    This option controls whether (1) or not (0) fapolicyd should create a usage statistics report on shutdown. The report is written to /var/log/fapolicyd-access.log. This report gives information about number of allowed accesses and denials. Then for both the subject and object cache, it dumps information about size, hits, misses, and evictions. The default value is 1 which means create the report.

detailed_report
    This option controls whether (1) or not (0) fapolicyd should add subject and object information to the usage statistics report. This would be information about the exact process or file path in the cache from most recently used to last recently used. This can be useful for forensics if an incident had occurred. But if the file names are sensitive then you may want to turn this off. The default value is 1 meaning add the details.

db_max_size
    This option controls how many megabytes to allow the trust database to grow to. If you have lots of packages installed, then you want to make it bigger. The default value is "auto", which tells the daemon to size the trust database based on current utilization whenever it starts or rebuilds the database. Auto sizing starts from a 100 megabyte baseline, targets roughly 75% active database usage, keeps lower-utilization reload headroom for the current trust database generation and the candidate generation being built, grows when needed, and shrinks conservatively when utilization is low. Manual numeric values are never changed by the daemon. If a manual value is too small for a safe reload, fapolicyd logs a warning with the current size and a recommended minimum. Set db_max_size to at least that recommendation, or use db_max_size = auto so the daemon can resize the LMDB map as package sets change.

subj_cache_size
    This option controls how many entries the subject cache holds. You want the size to be big enough that you are not getting too many evictions compared to hits. But you don't want to waste memory. Whenever there is an eviction, fapolicyd has to regenerate information about the subject and this slows performance. There are only 64k processes allowed at any time, so this would be the upper limit. The default value is 4099. With multiple decision_threads , this value is per worker. Leaving it unchanged increases total subject cache capacity and memory. Reducing it to keep the memory footprint stable can increase subject collisions, early subject cache evictions, and subject defer fallbacks.

obj_cache_size
    This option controls how many entries the object cache holds. You want the size to be big enough that you are not getting too many evictions compared to hits. But you don't want to waste memory. Whenever there is an eviction, fapolicyd has to regenerate information about the object and this slows performance. The default value is 8191. With multiple decision_threads , this value is per worker. Leaving it unchanged increases total object cache capacity and memory. Reducing it to keep the memory footprint stable can increase object cache misses, collisions, and evictions.

watch_fs
    This is a comma separated list of file systems that should be watched for access permission. No attempt is made to validate the file systems names. They should exactly match the name presented in the first column of /proc/mounts. If this is not configured, it will default to watching ext4, xfs, and tmpfs.

ignore_mounts
    ignore_mounts A comma-separated list of mount points that fapolicyd must not watch, even when their filesystem type matches watch_fs. Entries must be absolute paths exactly as shown in the second column of /proc/mounts; whitespace around commas is ignored. Each listed mount must be mounted with the noexec option; otherwise the daemon warns and monitors the mount point instead. The root filesystem / is always monitored. This option cannot be combined with allow_filesystem_mark=1. See the discussion in SECURITY CONSIDERATIONS FOR ignore_mounts.

trust
    This is a comma separated list of trust back-ends. If this is not configured, 'rpmdb,file' is default. Fapolicyd supports file back-end that reads content of /etc/fapolicyd/fapolicyd.trust and use it as a list of trusted files. The second option is rpmdb backend that generates list of trusted files from rpmdb.

integrity
    This option tells fapolicyd which integrity strategy it should use. It can be one of 4 values:

    none
        This is the default and does no integrity checking.

    size
        Selecting this option will compare the size of the file with what it was knows to be. This is better than nothing and very fast since fapolicyd already collects size information during normal processing. However, an attacker could replace the file and as long as the size matches, it will not be detected.

    ima Selecting this option will use a hash that the IMA subsystem places in a file's extended attributes in addition to the size check. IMA measurements can be SHA256 or SHA512 depending on kernel policy. When the IMA digest and trust metadata disagree, fapolicyd recomputes the IMA hash for a single retry before logging rate-limited warnings. The recomputation adds hashing overhead on the first mismatch and there is currently no configuration knob to disable these warnings. This means that all file systems holding executable code must support extended attributes.

    sha256
        Selecting this option will calculate a SHA256 hash by cryptographic means. A size check will also be performed.

syslog_format
    This option controls how the output from the access decision is formatted. The format is a comma separated list of subject and object names from the rules. It does not allow the keyword "all". It also allows for rule, dec, and perm. The format must include a semi-colon to delineate subject from object keywords. The typical use is to place information about the access decision, then subject information, a colon, and the object information. Also note that the more things being logged, the more it will impact system performance. Also, the event written is limited to 512 bytes. Example:
    syslog_format = rule,dec,perm,auid,pid,exe,:,path,ftype,trust

rpm_sha256_only
    When this option is set to 1, it will force RPM trust entries to use SHA256 or larger hashes. This is useful on systems where the integrity is set to SHA256 or IMA and some rpms were originally built with e.g. SHA1. The daemon will ignore these SHA1 entries when the RPM backend imports trust data. Hash integrity lookups also reject SHA1/MD5 records that are already present in the active trust database, so stale weak RPM entries do not remain trusted after a configuration reload enables this option. If set to 0 the daemon stores and uses SHA1/MD5 from RPM trust data as well. This is compatible with older behavior which works with the integrity set to NONE and SIZE. The NONE or SIZE integrity setting considers the files installed via rpm as trusted and it does not care about their hashes at all. The default value is 0.

allow_filesystem_mark
    When this option is set to 1, it allows fapolicyd to monitor file access events on the underlying file system when they are bind mounted or are overlayed (e.g. the overlayfs). Normally they block fapolicyd from seeing events on the underlying file systems. This may or may not be desirable. For example, you might start seeing containers accessing things outside of the container but there is no source of trust for the container. In that case you probably do not want to see access from the container. Or maybe you do not use containers but want to control anything run by systemd-run when dynamic users are allowed. In that case you probably want to turn it on. Not all kernel's support this option. Therefore the default value is 0. This option cannot be used when ignore_mounts lists one or more paths. Filesystem marks extend monitoring beneath bind or overlay mounts in a way that prevents individual mount points from being ignored. When both options appear in the configuration the daemon terminates with an error so the conflict can be corrected before startup.

report_interval
    This option specifies a reporting interval, measured in seconds, which fapolicyd uses to schedule recurring dumps of daemon state to fapolicyd.state and runtime metrics to fapolicyd.metrics. See fapolicyd.state(5) and fapolicyd.metrics(5) for the report fields. The default value of 0 disables interval reporting.

reset_strategy
    This option controls whether runtime metric counters are reset as part of metrics report generation. The default value is never, which preserves the historical behavior where metrics grow for the lifetime of the daemon. Use auto when interval reports should describe only the activity since the previous timer-based report. Use manual when counters should reset only after a signal-based report carries reset intent, such as fapolicyd-cli --reset-metrics. Plain fapolicyd-cli --check-status and fapolicyd-cli --check-metrics reports do not reset counters. Signal-based reports do not reset counters when this option is set to auto, and interval timer reports do not reset counters when it is set to manual. Set this option to never when continuously growing counters are required, and to auto or manual when reports should atomically snapshot the current metrics and start the next reporting interval with fresh counters. Rule hit counters are naturally scoped to the active ruleset generation and reset when a new ruleset is loaded; metric resets also clear them after reporting so the existing rules can be tested from a fresh counter window. In all reset modes, configuration and state identity values such as cache sizes, queue size, trust database size, integrity mode, permissive mode, watched mounts, and ruleset generation are not reset.

timing_collection
    This option controls whether privileged manual decision timing windows are allowed. The default value is off, which ignores timing start and stop requests. Set it to manual to allow root to use fapolicyd-cli --timing-start and fapolicyd-cli --timing-stop for bounded diagnostic timing runs. While a run is active, the daemon records fixed aggregate latency metrics for each decision worker and stage. When the run is stopped, the daemon writes /run/fapolicyd/fapolicyd.timing. Normal state reports include only timing control state, not the timing histograms. See fapolicyd.timing(5) for the timing report fields.

DECISION WORKER RESOURCE TUNING
Do not treat decision_threads as only a CPU setting. A higher value creates more decision workers, and each worker preallocates its own queue, subject cache, object cache, and subject-slot defer array. The subject defer array is sized from subj_cache_size with a fixed minimum, so increasing workers also increases total defer capacity and memory.

Increase decision_threads when metrics show that decision work is backing up, such as high queue wait, high Inter-thread max queue depth relative to q_size, or non-zero Inter-thread queue full count. After changing it, compare fapolicyd-cli(8) status or metrics reports before and after the restart. Watch queue depth, queue full count, subject and object cache collisions and evictions, subject defer fallbacks, and the reported glibc heap usage.

On systems with enough memory, keep q_size, subj_cache_size, and obj_cache_size unchanged when adding workers so total queue and cache capacity grows with the available decision parallelism. On memory-constrained systems, reduce those per-worker values only after estimating the total footprint. Reducing cache sizes can keep memory more stable, but it may increase cache misses, collisions, evictions, and subject defer fallbacks. Any sustained non-zero subject defer fallback count means the subject cache and derived defer array are too small for the workload.

RELOAD BEHAVIOR
On SIGHUP, fapolicyd parses fapolicyd.conf, publishes a new immutable decision configuration generation, reloads the filter configuration, and asks the normal rule and trust database owners to reload their state. A decision that has already started keeps using the decision configuration generation it pinned at the beginning of the decision. New decisions use the most recently published generation.

The following fapolicyd.conf settings are live after a successful reload:

    •   permissive, integrity, and the lookup-side rpm_sha256_only digest floor are decision-used fields and are published together as one immutable generation.

    •   nice_val, do_stat_report, detailed_report, reset_strategy, and timing_collection are applied directly by the reload path.

    •   syslog_format is used by the next successfully published ruleset.

    •   trust and the rpm_sha256_only RPM ingestion filter are used by the next trust database reload.

The fapolicyd-filter.conf file is also reloaded on SIGHUP before the trust database reload is requested. The filter is consulted when trust source entries are imported or rebuilt; it is not consulted directly by normal access decisions.

The following settings require a daemon restart because they are consumed when long-lived runtime objects are created:

    •   q_size, decision_threads, subj_cache_size, and obj_cache_size size the per-worker event queues, worker count, caches, and subject defer arrays.

    •   uid and gid control the daemon identity selected during startup.

    •   watch_fs, ignore_mounts, and allow_filesystem_mark determine the fanotify mark set installed during startup.

    •   db_max_size and the special auto database sizing mode determine the LMDB map size policy used when the trust database is opened or rebuilt. Changing this setting in the file does not replace the active database sizing policy until restart.

    •   report_interval starts the interval report timer used by the decision thread.

  SECURITY CONSIDERATIONS FOR ignore_mounts
Ignoring a mount removes fanotify visibility for that tree. fapolicyd will not evaluate reads/opens that occur on the ignored mount, which reduces load but creates blind spots in policy enforcement.

•   Interpreters and plugins: Even with noexec, trusted interpreters (shell, Python, Java, Node.js, etc.) and applications that load plugins, bytecode, or data-driven modules may read and act on files from the ignored mount. Those accesses bypass fapolicyd because no fanotify mark is placed there.

•   Policy blind spots: Content copied into the ignored tree is not evaluated while it resides there. Risk may surface only after the content moves to a monitored location.

•   Coverage of system paths: The root filesystem / is always monitored so core paths (e.g., /usr) remain protected. Do not rely on ignore_mounts to work around denials for native ELF binaries; it is a performance control, not a permissive toggle.

Before adding entries to ignore_mounts, administrators should:

    •   Ensure each mount is truly data-only and is mounted with noexec.

    •   Run the advisory check:
        fapolicyd-cli --check-ignore_mounts[=MOUNT]
        to verify the mount exists, confirm noexec, and scan for executable regular files, ELF/shared objects, archives/JARs/ZIPs, bytecode caches, plugin/runtime directories, and files matching the %languages macro. The command reports category counts and returns a non-zero status when potentially executable content is detected.

    •   Reevaluate after workload changes; caches and logging trees evolve over time.

Matching is by mount point path as shown in /proc/mounts; trailing slashes are normalized. Bind/overlay/NFS/FUSE mounts are matched by their mount point path (not device identifiers). When allow_filesystem_mark=1 is set together with ignore_mounts, the daemon refuses the configuration to avoid conflicting semantics.

SEE ALSO
fapolicyd(8), fapolicyd-cli(8), fapolicyd.state(5), fapolicyd.metrics(5), fapolicyd.timing(5), and fapolicyd.rules(5).

AUTHOR
Steve Grubb