]> Networking Core Core. Receive buffer default NET-CORE-RMEM-DEFAULT Spinbutton 65535 262140 -1 /proc/sys/net/core/rmem_default Networking Core Core. Receive buffer maximum NET-CORE-RMEM-MAX Spinbutton 65535 262140 -1 /proc/sys/net/core/rmem_max Networking Core Core. Send buffer default NET-CORE-WMEM-DEFAULT Spinbutton 65535 262140 -1 /proc/sys/net/core/wmem_default Networking Core Core. Send buffer maximum NET-CORE-WMEM-MAX Spinbutton 65535 262140 -1 /proc/sys/net/core/wmem_max Networking TCP TCP [1]. FIN timeout NET-TCP-FIN-TIMEOUT Spinbutton 100 500 -1 /proc/sys/net/ipv4/tcp_fin_timeout FIN timeout: The number of seconds to wait for a final FIN before the socket is always closed. This is a violation of the TCP standard but required for prevention of some denial of service attacks. Networking TCP TCP [1]. Keepalive time NET-TCP-KEEPALIVE-TIME Spinbutton 0 65535 -1 /proc/sys/net/ipv4/tcp_keepalive_time Keepalive time: How often TCP sends out a keep alive message (in seconds). (Only when keep alive is enabled). Networking TCP TCP [1]. Number of keepalive probes NET-TCP-KEEPALIVE-PROBES Spinbutton 0 50 -1 /proc/sys/net/ipv4/tcp_keepalive_probes Number of keepalive probes: The number of probes that TCP sends out before it decides that a connection is broken. Networking TCP TCP [1]. Maximum keepalive probes NET-TCP-MAX-KEEPALIVES Spinbutton 0 30 -1 /proc/sys/net/ipv4/tcp_max_ka_probes Maximum keepalive probes: Holds the number of probes that are sent out per slow timer run. This shouldn't be set too high to prevent bursts. Networking TCP TCP [1]. Maximum SYN retransmit. NET-TCP-SYN-RETRIES Spinbutton 5 255 -1 /proc/sys/net/ipv4/tcp_syn_retries SYN Retries: Number of times initial SYNs for a TCP connection attempt will be retransmitted. This is only the timeout for outgoing connections. For incoming connections, see retries1 Networking TCP TCP [1]. Maximum SYN backlog. NET-TCP-SYN-BACKLOG Spinbutton 0 512 -1 /proc/sys/net/ipv4/tcp_max_syn_backlog Maximum SYN backlog: Length of the per-socket backlog queue. When the queue is full, and there are more connection requests, Linux will drop the incoming packets. When SYN Cookies are enabled the backlog queue is effectively ignored. Networking TCP TCP [1]. Maximum retransmit answer retries. NET-TCP-RETRIES1 Spinbutton 0 64 -1 /proc/sys/net/ipv4/tcp_retries1 Retries 1: Defines how often an answer to a TCP connection is retransmitted before giving up. Networking TCP TCP [1]. Maximum retransmit retries. NET-TCP-RETRIES2 Spinbutton 0 64 -1 /proc/sys/net/ipv4/tcp_retries2 Retries 2: Defines how often a TCP packet is retransmitted before giving up. Networking TCP TCP [2]. Enable TCP Syncookies NET-TCP-SYNCOOKIES Checkbox 0 /proc/sys/net/ipv4/tcp_syncookies Syncookies: This option causes 'SYN Cookies' to be sent when the SYN backlog que of a socket overflows. This prevents possible denial of service attacks. Note, that the concept of a socket backlog is abandoned, which means the peer may not recieve reliable error messages from an overloaded server with SYN Cookies enabled. Networking TCP TCP [2]. Retransmit collapse NET-TCP-RETRANS-COLLAPSE Checkbox 0 /proc/sys/net/ipv4/tcp_retrans_collapse Retransmit collapse: This option enables bug-to-bug compatability with some broken printers. On retransmit it tries to send bigger packets to work around bugs in certain TCP stacks. Can be turned off if your printer works fine without it, or you don't have a networked printer. Networking TCP TCP [2]. Select Acknowledgements NET-TCP-SACK Checkbox 0 /proc/sys/net/ipv4/tcp_sack Select Acknowledgements: This option enables select acknowledgements (See RFC2018). Networking TCP TCP [2]. TCP Timestamping NET-TCP-TIMESTAMPS Checkbox 0 /proc/sys/net/ipv4/tcp_timestamps Timestamps: This option enables TCP Timestamping for each packet. (See RFC1323). Networking TCP TCP [2]. TCP Window scaling NET-TCP-WINDOW-SCALING Checkbox 0 /proc/sys/net/ipv4/tcp_window_scaling Window scaling: This option enables TCP window scaling (See RFC1323). Networking ICMP ICMP [1]. Destination unreachable rate NET-ICMP-DESTUNREACHRATE Spinbutton 100 500 -1 /proc/sys/net/ipv4/icmp_destunreach_rate Networking ICMP ICMP [1]. Echo reply rate NET-ICMP-ECHOREPLYRATE Spinbutton 0 500 -1 /proc/sys/net/ipv4/icmp_echoreply_rate Networking ICMP ICMP [1]. Param prob rate NET-ICMP-PARAMPROBRATE Spinbutton 100 500 -1 /proc/sys/net/ipv4/icmp_paramprob_rate Networking ICMP ICMP [1]. Time exceed rate NET-ICMP-TIMEEXCEEDRATE Spinbutton 100 500 -1 /proc/sys/net/ipv4/icmp_timeexceed_rate Networking ICMP ICMP [2]. Ignore extraneous error messages NET-ICMP-IGNOREBOGUSERRORS Checkbox -1 /proc/sys/net/ipv4/icmp_ignore_bogus_error_responses Extraneous messages: This option ignores all bogus error messages that may arrive. Networking ICMP ICMP [2]. Ignore all messages NET-ICMP-ECHOIGNOREAL Checkbox -1 /proc/sys/net/ipv4/icmp_echo_ignore_all Ignore all: This option will ignore all ICMP traffic arriving on all ethernet devices. Networking ICMP ICMP [2]. Ignore broadcast messages NET-ICMP-ECHOIGNOREBROADCASTS Checkbox -1 /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts Ignore broadcast: This option will ignore ICMP broadcast messages on all ethernet devices. Networking IP IP [1]. Default time to live (TTL) NET-IP-DEFAULT-TTL Spinbutton 8 256 -1 /proc/sys/net/ipv4/ip_default_ttl Default TTL: The maximum number of hops a packet may travel. Networking IP IP [1]. Time to hold IP fragment in memory NET-IP-FRAGTIME Spinbutton 10 60 -1 /proc/sys/net/ipv4/ipfrag_time Fragtime: The number of seconds an IP fragment should remain in memory. Networking IP IP [2]. IP Forwarding NET-IP-FORWARDING Checkbox -1 /proc/sys/net/ipv4/ip_forward IP Forwarding: This option enables forwarding of IP packages. E.g. from eth0 to eth1. Networking IP IP [2]. RP Filter NET-IP-RP-FILTER Checkbox -1 /proc/sys/net/ipv4/conf/all/rp_filter RP Filter: Enables source route verification Networking IP IP [2]. Global path MTU discovery disable NET-IP-NO-PMTU Checkbox -1 /proc/sys/net/ipv4/ip_no_pmtu_disc MTU discovery: Enabling this option will turn off path MTU discovery (MTU is the Maximum Transmission Unit) Networking IP IP [2]. Always defragment incoming IP packets NET-IP-ALWAYS-DEFRAG Checkbox -1 /proc/sys/net/ipv4/ip_always_defrag Defragment: All incoming fragments (parts of IP packets that arose when some host between source and destination decided that the packets were too large and cut them into pieces) will be reassembled (defragmented) before being processed, even if the packet is to be forwarded. Networking IP IP [2]. Debugging of IP Masquerading NET-IP-MASQ-DEBUG Checkbox -1 /proc/sys/net/ipv4/ip_masq_debug IP_Masq debug: This option toggles debug message output for IP masquerading. Networking Unix domain Unix domain Delete delay NET-UNIX-DELETE-DELAY Spinbutton 1 60 -1 /proc/sys/net/unix/delete_delay Delete delay: Time in seconds to wait after closure before first attempting to delete a unix domain socket Networking Unix domain Unix domain Destroy delay NET-UNIX-DESTROY-DELAY Spinbutton 1 60 -1 /proc/sys/net/unix/destroy_delay Delete delay: Time in seconds to wait after closure between repeat attempts to destroy a unix domain socket Networking Unix domain Unix domain Max Datagram Queue Length NET-UNIX-MAX-DGRAM-QLEN Spinbutton 5 100 -1 /proc/sys/net/unix/max_dgram_qlen Max Datagram Queue Length: Sets the maximum number of datagram messages that may be pending on a Unix domain socket before further writes block or error. Networking Token Ring Timeouts RIF Cache Timeout NET-IP-MASQ-DEBUG Spinbutton 20000 1000000 -1 /proc/sys/net/token-ring/rif_timeout RIF timeout: Controls the number of hundredths of seconds before RIF routing cache entries for the token ring subsystem are purged. File systems Core File system Core dquota-max FS-DQUOT-MAX Spinbutton 0 8192 0 /proc/sys/fs/dquot-max dquota-max: Holds the maximum number of cached disk quota entries. Should be increased if you have many simultaneous users. File systems Core File system Core file-max FS-FILE-MAX Spinbutton 0 16384 0 /proc/sys/fs/file-max file-max: The value in file-max denotes the maximum number of file handles that the Linux kernel will allocate. When you get a lot of error messages about running out of file handles, you might want to raise this limit. The default value is 4096. File systems Core File system Core inode-max FS-INODE-MAX Spinbutton 0 65535 0 /proc/sys/fs/inode-max inode-max: The maximum number of inodes possible to use. You should set this to two or three times higher than file-max. File systems Core File system Core super-max FS-SUPER-MAX Spinbutton 0 1024 0 /proc/sys/fs/super-max super-max: The maximum number of superblocks that may be used. One superblock is used each time you mount a filesystem. Virtual Memory bdflush bdflush. Activate bdflush when % dirty VM-BDFLUSH-NFRACT Spinbutton 0 100 0 /proc/sys/vm/bdflush Virtual Memory bdflush bdflush. Dirty blocks to write per wake cycle. VM-BDFLUSH-NDIRTY Spinbutton 50 1000 1 /proc/sys/vm/bdflush Virtual Memory bdflush bdflush. Try to reclaim n buffers on refill VM-BDFLUSH-NREFILL Spinbutton 64 1024 2 /proc/sys/vm/bdflush Virtual Memory bdflush bdflush. Dirty buffer threshold VM-BDFLUSH-NREF-DIRT Spinbutton 256 1024 3 /proc/sys/vm/bdflush Virtual Memory bdflush bdflush. Time to age normal buffer before flush VM-BDFLUSH-AGE-BUFFER Spinbutton 500 5000 5 /proc/sys/vm/bdflush Virtual Memory bdflush bdflush. Time to age superblock before flush VM-BDFLUSH-AGE-SUPER Spinbutton 100 5000 6 /proc/sys/vm/bdflush Virtual Memory Buffermem Buffermem. Minimum percentage VM-BUFFERMEM-MIN Spinbutton 1 50 0 /proc/sys/vm/buffermem Virtual Memory Buffermem Buffermem. Maximum percentage VM-BUFFERMEM-MAX Spinbutton 0 1024 2 /proc/sys/vm/buffermem Virtual Memory Buffermem Page Cache. Minimum percentage VM-PAGECACHE-MIN Spinbutton 1 50 0 /proc/sys/vm/pagecache Virtual Memory Buffermem Page Cache. Maximum percentage VM-PAGECACHE-MAX Spinbutton 10 90 2 /proc/sys/vm/pagecache Virtual Memory Swapping Overcommit. Overcommit Memory VM_OVERCOMMIT Checkbox -1 /proc/sys/vm/overcommit_memory Overcommit Memory: The following algorithm is used to decide if there's enough memory: if this option is checked, then there's always enough memory. This is a useful feature, since programs often malloc() huge amounts of memory 'just in case', while they only use a small part of it. Leaving this option unchecked will lead to the failure of such a huge malloc(), when in fact the system has enough memory for the program to run. On the other hand, enabling this feature can cause you to run out of memory and thrash the system to death, so large and/or important servers will want to set this disabled. Virtual Memory Swapping kswapd. Tries base VM-KSWAPD-TRIES-BASE Spinbutton 512 1024 0 /proc/sys/vm/kswapd Tries base: The maximum number of pages kswapd tries to free in one round. This value is divided by 4 or 8. Virtual Memory Swapping kswapd. Tries min VM-KSWAPD-TRIES-MIN Spinbutton 16 128 1 /proc/sys/vm/kswapd Tries min: The minimum number of times kswapd tries to free a page. Virtual Memory Swapping kswapd. Swap cluster VM-KSWAPD-SWAP-CLUSTER Spinbutton 32 256 2 /proc/sys/vm/kswapd Swap cluster: This is the number of pages kswapd writes in one turn. This value should be large so that kswapd does its IO in large chunks, but not so large that it floods the request queue. Virtual Memory Swapping VM [2]. Page cluster VM-VM2-PAGE-CLUSTER Spinbutton 1 5 -1 /proc/sys/vm/page-cluster This entry configures the swap readahead. 1 << PAGE-CLUSTER Virtual Memory Pagetable cache Page table cache. Minimum VM-PAGETABLE-CACHE-MIN Spinbutton 0 90 0 /proc/sys/vm/pagetable_cache pagetablecache settings: The kernel keeps a number of page tables in a per-CPU cache. This helps a lot on SMP systems. The cache size for each processor will be between the min and max value. On a low memory (<16mb) single CPU system, you can safely set these values to 0 so you don't waste memory. Virtual Memory Pagetable cache Page table cache. Maximum VM-PAGETABLE-CACHE-MAX Spinbutton 0 90 1 /proc/sys/vm/pagetable_cache Kernel Security Security Disable ctrl-alt-del KERNEL-CTRL-ALT-DEL Checkbox 0 /proc/sys/kernel/ctrl-alt-del Control Alt Delete: When this is unchecked, ctrl-alt-del is trapped and sent to the init(1) program to handle a graceful restart. However, when this is checked, Linux's reaction to this key combination will be an immediate reboot, without syncing its dirty buffers. Kernel Security Security Enable 'magic sysrq' KERNEL-SYSRQ Checkbox 0 /proc/sys/kernel/sysrq Enable Magic SysRQ: In most environments it is not be desirable to allow end users to use the console debugging sequences. This option enables the magic key sequences which may be useful when doing kernel development or debugging a system problem. Kernel Logging Logging Reboot time after a panic KERNEL-PANIC Spinbutton 0 3600 0 /proc/sys/kernel/panic Panic reboot time: After a kernel panic the kernel will wait this long before attempting to reboot the system. Normally this is set to zero to disable the feature, but for a remote machine you may wish to set this. Kernel Logging Logging Space to resume accounting KERNEL-ACCT-RESUME Spinbutton 1 99 0 /proc/sys/kernel/acct Accounting resume: If accounting is stopped due to lack of disk space it will be resumed when a check finds the log disk has this percentage of space free. Kernel Logging Logging Suspend accounting KERNEL-ACCT-SUSPEND Spinbutton 1 99 1 /proc/sys/kernel/acct Suspend accounting: When the log disk drops to this percentage of free space then accounting is suspended. Kernel Logging Logging Accounting space timer KERNEL-ACCT-TIMER Spinbutton 1 3600 2 /proc/sys/kernel/acct Accounting space timer: Controls how often in seconds the disk space is checked in order to resume accounting when the disk becomes too full. Kernel Logging Logging Console log level KERNEL-PRINTK-CONSOLE-LOGLEVEL Spinbutton 0 7 0 /proc/sys/kernel/printk Console log level: Sets the priority level needed before a message is printed to the console. Kernel Resources Resources Real time signals KERNEL-RTSIG-MAX Spinbutton 100 5000 0 /proc/sys/kernel/rtsig-max Real Time Signals: Some processes use real time signal queues. These queues have a finite length to control resource usage. If you have real time signal using applications reporting insufficient signals you may need to adjust this. Kernel Resources Resources Maximum System 5 Shared Memory KERNEL-SHMALL Spinbutton 1048576 2147483647 0 /proc/sys/kernel/shmall Maximum SYSV Shared Memory: Set the limit on the total amount of system 5 style shared memory in the system. Some large database applications such as Oracle may require this is raised from the default. Kernel Resources Resources Maximum System 5 Segment Size KERNEL-SHMMAX Spinbutton 16384 33554432 0 /proc/sys/kernel/shmmax Maximum SYSV Shared Memory segment size: Set the limit on the size of each system 5 style shared memory object in the system. Some large database applications such as Oracle may require this is raised from the default. Hardware RAID RAID settings Min speed limit HARDWARE-RAIDMIN Spinbutton 100 1000 0 /proc/sys/dev/raid/speed_limit_min Minimum level throughput. Hardware RAID RAID settings Max speed limit HARDWARE-RAIDMAX Spinbutton 100000 200000 0 /proc/sys/dev/raid/speed_limit_max Maximum level throughput.