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Controlling the User Cache

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Controlling the User Cache

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User credentials are cached in memory on each node to avoid connecting to a remote authentication service or hitting the disk for every incoming request. You can configure characteristics of the user cache with the cache.ttl, cache.max_users, and cache.hash_algo realm settings.

PKI realms do not use the user cache.

The cached user credentials are hashed in memory. By default, X-Pack security uses a salted sha-256 hash algorithm. You can use a different hashing algorithm by setting the cache_hash_algo setting to any of the following:

Table 6. Cache hash algorithms

Algorithm			Description
`ssha256`			Uses a salted `sha-256` algorithm (default).
`md5`			Uses `MD5` algorithm.
`sha1`			Uses `SHA1` algorithm.
`bcrypt`			Uses `bcrypt` algorithm with salt generated in 1024 rounds.
`bcrypt4`			Uses `bcrypt` algorithm with salt generated in 16 rounds.
`bcrypt5`			Uses `bcrypt` algorithm with salt generated in 32 rounds.
`bcrypt6`			Uses `bcrypt` algorithm with salt generated in 64 rounds.
`bcrypt7`			Uses `bcrypt` algorithm with salt generated in 128 rounds.
`bcrypt8`			Uses `bcrypt` algorithm with salt generated in 256 rounds.
`bcrypt9`			Uses `bcrypt` algorithm with salt generated in 512 rounds.
`noop`,`clear_text`			Doesn’t hash the credentials and keeps it in clear text in memory. CAUTION: keeping clear text is considered insecure and can be compromised at the OS level (for example through memory dumps and using `ptrace`).

Evicting Users from the Cache

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X-Pack security exposes a Clear Cache API you can use to force the eviction of cached users. For example, the following request evicts all users from the ad1 realm:

$ curl -XPOST 'http://localhost:9200/_xpack/security/realm/ad1/_clear_cache'

To clear the cache for multiple realms, specify the realms as a comma-separated list:

$ curl -XPOST 'http://localhost:9200/_xpack/security/realm/ad1,ad2/_clear_cache'

You can also evict specific users:

$ curl -XPOST 'http://localhost:9200/_xpack/security/realm/ad1/_clear_cache?usernames=rdeniro,alpacino'

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