


Regarding the problem of too many Session files in PHP, _PHP Tutorial
Regarding the problem of too many Session files in PHP,
PHP’s default mechanism: for every php request, there will be a 1/100 probability (default value) of triggering "session recycling" ". If "session recycling" occurs, the /tmp/sess_* files will be checked. If the last modification time exceeds 1440 seconds (the value of gc_maxlifetime), they will be deleted, which means that these sessions have expired
1. What is a session file
The file is generally /tmp/sessions/sess_4b1e384ad74619bd212e236e52a5a174If
username|s:9:"test";admin|s:1:"0";
2. When does session recycling occur?
By default, for every php request, there will be a 1/100 probability of recycling, so it may be simply understood as "one recycling occurs for every 100 php requests." This probability is controlled by the following parameters
#概率是gc_probability/gc_divisor session.gc_probability = 1 session.gc_divisor = 100
-
Assume that in this case gc_maxlifetime=120, if a session file was last modified 120 seconds ago, then the session will still be valid before the next recycling (1/100 probability) occurs.
-
If your session uses session.save_path to save the session elsewhere, the session recycling mechanism may not automatically process expired session files. At this time, you need to delete expired sessions manually (or crontab) regularly
3. Set the session storage directory
If you use php5-fpm, modify /etc/php5/fpm/php.ini
, modify or add the following line:
session.save_path = 3;600:/tmp/sessions
4. Session clearing script
#!/bin/sh find /tmp/php-session -cmin +24 -name "sess_*" -and -size 0 -delete > /dev/null 2>&1 find /tmp/php-session -cmin +1440 -name "sess_*" -delete > /dev/null 2>&1
We can get the time here through session.gc_maxlifetime, just put it in the scheduled task (crontab)
Other ways
-
Use memcache, etc., (session.save_handler = memcache)
-
Use cookies, but the cookies must be encrypted
5. Use tmfs to store session
1. Mount /tmp as tmpfs file system
Modify /etc/fstab and add the following content to the last line: /tmp/sessions tmpfs defaults,size=5120m 0 0
mount -a
2. Create session storage folder
php will not automatically create these folders, but some scripts for creating folders are provided in the source file. The script below is also easy to use. The content of the script is as follows
#!/bin/sh dir="0 1 2 3 4 5 6 7 8 9 a b c d e f" for levela in $dir; do for levelb in $dir; do for levelc in $dir; do mkdir -p /tmp/sessions/$levela/$levelb/$levelc; done done; done chown -R root:webgrp /tmp/sessions && chmod -R 1777 /tmp/sessions
Because /tmp/sessions is used for memory, all files in it will be lost after the server is restarted. Therefore, the above script needs to be added to /etc/rc.local and placed before starting php
3. Store sessions in different directories
php itself supports multi-level hashing of sessions. In php.ini, change ;session.save_path = /tmp to
session.save_path = "3;/tmp/sessions
4. Session recycling
Use the script above

In PHP, you can use session_status() or session_id() to check whether the session has started. 1) Use the session_status() function. If PHP_SESSION_ACTIVE is returned, the session has been started. 2) Use the session_id() function, if a non-empty string is returned, the session has been started. Both methods can effectively check the session state, and choosing which method to use depends on the PHP version and personal preferences.

Sessionsarevitalinwebapplications,especiallyfore-commerceplatforms.Theymaintainuserdataacrossrequests,crucialforshoppingcarts,authentication,andpersonalization.InFlask,sessionscanbeimplementedusingsimplecodetomanageuserloginsanddatapersistence.

Managing concurrent session access in PHP can be done by the following methods: 1. Use the database to store session data, 2. Use Redis or Memcached, 3. Implement a session locking strategy. These methods help ensure data consistency and improve concurrency performance.

PHPsessionshaveseverallimitations:1)Storageconstraintscanleadtoperformanceissues;2)Securityvulnerabilitieslikesessionfixationattacksexist;3)Scalabilityischallengingduetoserver-specificstorage;4)Sessionexpirationmanagementcanbeproblematic;5)Datapersis

Load balancing affects session management, but can be resolved with session replication, session stickiness, and centralized session storage. 1. Session Replication Copy session data between servers. 2. Session stickiness directs user requests to the same server. 3. Centralized session storage uses independent servers such as Redis to store session data to ensure data sharing.

Sessionlockingisatechniqueusedtoensureauser'ssessionremainsexclusivetooneuseratatime.Itiscrucialforpreventingdatacorruptionandsecuritybreachesinmulti-userapplications.Sessionlockingisimplementedusingserver-sidelockingmechanisms,suchasReentrantLockinJ

Alternatives to PHP sessions include Cookies, Token-based Authentication, Database-based Sessions, and Redis/Memcached. 1.Cookies manage sessions by storing data on the client, which is simple but low in security. 2.Token-based Authentication uses tokens to verify users, which is highly secure but requires additional logic. 3.Database-basedSessions stores data in the database, which has good scalability but may affect performance. 4. Redis/Memcached uses distributed cache to improve performance and scalability, but requires additional matching

Sessionhijacking refers to an attacker impersonating a user by obtaining the user's sessionID. Prevention methods include: 1) encrypting communication using HTTPS; 2) verifying the source of the sessionID; 3) using a secure sessionID generation algorithm; 4) regularly updating the sessionID.


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