DOTSLASHLINUX

Kernel Sources:       sys-kernel/gentoo-sources

Kernel Version:       4.14.12

Last Updated on:      06/01/2018

Update Notice:        1- Excluded 'CONFIG_PAGE_TABLE_ISOLATION' in 'Security options --->'
                      2- Included 'CONFIG_STANDALONE' in 'Device Drivers  --->'
                      3- Included 'CONFIG_PREVENT_FIRMWARE_BUILD' in 'Device Drivers  --->'
                      4- Included 'CONFIG_X86_5LEVEL' in 'Processor type and features  --->'
                      5- Included 'CONFIG_ORC_UNWINDER' in 'Kernel hacking  --->'
                      6- Excluded QEMU-virtualization-related options in favor of VirtualBox
                      7- Excluded swap-related options
                      8- Excluded 32-bit support
                      9- Switched from XFS to EXT4

Priorities:           1- high performance
                      2- minimal
                      3- low memory footprint
                      4- small size
                      5- power saving
                      6- security
                      7- low-latency

Total Options:        2469 (grep -c 'CONFIG_' DOTSLASHLINUX.config)

Included Options:     645 (grep -c '=y' DOTSLASHLINUX.config)

Excluded Options:     1761 (grep -c 'is not set' DOTSLASHLINUX.config)

Final Size (LZ4):     5,644,240 Bytes

Patches Applied:      1- UKSM-4.14 Patch (https://github.com/dolohow/uksm/blob/master/uksm-4.14.patch)

Contributors:         Firas Khalil Khana [irc: firas] [email: firasuke@gmail.com]

Side Notes:           1- Options that aren't listed here are excluded [ ].
                      2- These guides provide users with a solid starting setup to build on.
                      3- These guides are constantly being updated.
                      4- If there's something I didn't explain properly or I misexplained
                         then please do let me know either by kindly leaving a comment below
                         or by sending me an email on: firasuke@gmail.com

The Linux Kernel Configuration Guide Part 3 - General setup --->

Before starting with the General setup section, there’s this important option just before it:

[∗] 64-bit kernel

Symbol:     CONFIG_64BIT

Help:       Say yes to build a 64-bit kernel - formerly known as x86_64
            Say no to build a 32-bit kernel - formerly known as i386

Type:       boolean

Choice:     built-in [∗]

Reason:     It's highly recommended that you include this option if you plan to
            use the custom built kernel on a 64-bit system.

---

1- General setup

() Cross-compiler tool prefix

Symbol:     CONFIG_CROSS_COMPILE

Help:       Same as running 'make CROSS_COMPILE=prefix-' but stored for
            default make runs in this kernel build directory.  You don't
            need to set this unless you want the configured kernel build
            directory to select the cross-compiler automatically.

Type:       string

Choice:     excluded ()

Reason:     You can safely exclude this option if you're not building this kernel
            for another machine (an ARM device perhaps).

[ ] Compile also drivers which will not load

Symbol:     CONFIG_COMPILE_TEST

Help:       Some drivers can be compiled on a different platform than they are
            intended to be run on. Despite they cannot be loaded there (or even
            when they load they cannot be used due to missing HW support),
            developers still, opposing to distributors, might want to build such
            drivers to compile-test them.
            
            If you are a developer and want to build everything available, say Y
            here. If you are a user/distributor, say N here to exclude useless
            drivers to be distributed.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely leave the value of this option empty if you don't plan
            to build drivers for different architectures as it's for developing purposes.

() Local version - append to kernel release

Symbol:     CONFIG_LOCALVERSION

Help:       Append an extra string to the end of your kernel version.
            This will show up when you type uname, for example.
            The string you set here will be appended after the contents of
            any files with a filename matching localversion∗ in your
            object and source tree, in that order.  Your total string can
            be a maximum of 64 characters.

Type:       string

Choice:     excluded ()

Reason:     You can safely leave the value of this option empty as it's only needed
            for those who build custom kernels and don't want to lose track of their
            kernels by appending extra strings to the end of the kernel's version.

[ ] Automatically append version information to the version string

Symbol:     CONFIG_LOCALVERSION_AUTO

Help:       This will try to automatically determine if the current tree is a
            release tree by looking for git tags that belong to the current
            top of tree revision.
            
            A string of the format -gxxxxxxxx will be added to the localversion
            if a git-based tree is found.  The string generated by this will be
            appended after any matching localversion∗ files, and after the value
            set in CONFIG_LOCALVERSION.

            (The actual string used here is the first eight characters produced
            by running the command:

              $ git rev-parse --verify HEAD

            which is done within the script "scripts/setlocalversion".)

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as CONFIG_LOCALVERSION should be
            sufficient for those who don't want to lose track of their custom
            built kernels.

Kernel compression mode (LZ4) —>

Make sure you have app-arch/lz4 installed before compiling your kernel.

Symbol:     CONFIG_KERNEL_LZ4

Help:       LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
            A preliminary version of LZ4 de/compression tool is available at
            <https://code.google.com/p/lz4>.
            
            Its compression ratio is worse than LZO. The size of the kernel
            is about 8% bigger than LZO. But the decompression speed is
            faster than LZO.

Type:       boolean

Choice:     built-in [∗]

Reason:     It's highly recommended that you include this option in your
            kernel as LZ4 provides the fastest decompression speed out of
            all compression methods and decompression speed is what matters
            when measuring boot times.

            Include this option if you're on a slow storage system (a 5400rpm
            HDD for example).

            If you're using an extremely fast storage system then you may tru
            CONFIG_KERNEL_XZ as it provides the smallest kernel size out of all
            compression methods and it may (although rarely) speed up boot time
            compared to LZ4 by an extremely small amount of time (less than 100ms).

            Furthermore, in some case using an uncompressed kernel slowed boot time down 
            by 300-500ms. Again if your storage is extremely fast then I suggest you use
            an uncompressed kernel (you can find several patches online for building an
            uncompressed kernel and I'll be talking about applying patches to the linux kernel
            really soon).

            Exclude every other compression method and make sure that you have the
            proper tools for compression to prevent errors from popping up.

(DOTSLASHLINUX) Default hostname

Symbol:     CONFIG_DEFAULT_HOSTNAME

Help:       This option determines the default system hostname before userspace
            calls sethostname(2). The kernel traditionally uses "(none)" here,
            but you may wish to use a different default here to make a minimal
            system more usable with less configuration.

Type:       string

Choice:     DOTSLASHLINUX

Reason:     It's recommended if your system's default hostname was set here (rather than
            relying on the hostname boot service) if you're building this kernel for your
            current system.

            You know what they say the less services you have at boot time, the faster your
            system boots.

[∗] Support for paging of anonymous memory (swap)

Symbol:     CONFIG_SWAP

Help:       This option allows you to choose whether you want to have support
            for so called swap devices or swap files in your kernel that are
            used to provide more virtual memory than the actual RAM present
            in your computer.  If unsure say Y.

Type:       boolean

Choice:     built-in [∗]

Reason:     It's highly recommended that you include this option in your kernel
            as swap is a must have feature on all systems.

            My system has 7.7 GiB of ram and idles at ~60MiB of ram on dwm so
            basically why use swap? It was until recently that I was forced to
            add swap space after running swapless builds for 2 years now.

            I had 9 jobs running, and was trying to build chromium from source, 
            while browsing the web on my seamonkey web browser. Suddenly my system 
            lagged horribly (I had my customization set to maximum throughput) and
            chromium stopped at about 60% saying it ran out of memory (virtual memory). 
            So yeah I had to reinstall gentoo to get my swap space up and running.

            After I learned my lesson the hard way, I'm now convinced that all systems
            need a swap partition.

            I went with 15.4 GiB of swap space since I tend to open lots of apps when
            compiling.

-∗- System V IPC

Symbol:     CONFIG_SYSVIPC

Help:       Inter Process Communication is a suite of library functions and
            system calls which let processes (running programs) synchronize and
            exchange information. It is generally considered to be a good thing,
            and some programs won't run unless you say Y here. In particular, if
            you want to run the DOS emulator dosemu under Linux (read the
            DOSEMU-HOWTO, available from <http://www.tldp.org/docs.html#howto>),
            you'll need to say Y here
            
            You can find documentation about IPC with "info ipc" and also in
            section 6.4 of the Linux Programmer's Guide, available from
            <http://www.tldp.org/guides.html>.

Type:       boolean

Choice:     built-in -∗-

Reason:     It's highly recommended that you include this option in your kernel
            (that is if it isn't already forcibly included by CONFIG_GENTOO_LINUX
            and CONFIG_GENTOO_LINUX_PORTAGE).

[ ] POSIX Message Queues

Symbol:     CONFIG_POSIX_MQUEUE

Help:       POSIX variant of message queues is a part of IPC. In POSIX message
            queues every message has a priority which decides about succession
            of receiving it by a process. If you want to compile and run
            programs written e.g. for Solaris with use of its POSIX message
            queues (functions mq_∗) say Y here.
            
            POSIX message queues are visible as a filesystem called 'mqueue'
            and can be mounted somewhere if you want to do filesystem
            operations on message queues
            
            If unsure, say Y.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you won't be compiling and 
            running programs written for Solaris that make use of its POSIX 
            queues.

[ ] Enable process_vm_readv/writev syscalls

Symbol:     CONFIG_CROSS_MEMORY_ATTACH

Help:       Enabling this option adds the system calls process_vm_readv and
            process_vm_writev which allow a process with the correct privileges 
            to directly read from or write to another process' address space.
            See the man page for more details.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you're sure that no application
            uses these system calls.

[∗] open by fhandle syscalls

Symbol:     CONFIG_FHANDLE

Help:       If you say Y here, a user level program will be able to map
            file names to handle and then later use the handle for
            different file system operations. This is useful in implementing
            userspace file servers, which now track files using handles instead
            of names. The handle would remain the same even if file names
            get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
            syscalls.

Type:       boolean

Choice:     built-in [∗]

Reason:     It's highly recommended that you include this option in your kernel
            (that is if it isn't already forcibly included by CONFIG_GENTOO_LINUX,
            CONFIG_GENTOO_LINUX_UDEV and CONFIG_GENTOO_LINUX_INIT_SYSTEMD).

            It's one of those options that causes headaches when excluded, as you'll
            probably overlook it when trying to determine the real cause behind your
            boot failure.

[ ] uselib syscall

Symbol:     CONFIG_USELIB

Help:       This option enables the uselib syscall, a system call used in the
            dynamic linker from libc5 and earlier.  glibc does not use this
            system call.  If you intend to run programs built on libc5 or
            earlier, you may need to enable this syscall.  Current systems
            running glibc can safely disable this.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you're on a modern system running
            a modern version of glibc.

[ ] Auditing support

Symbol:     CONFIG_AUDIT

Help:       Enable auditing infrastructure that can be used with another
            kernel subsystem, such as SELinux (which requires this for
            logging of avc messages output).  System call auditing is included
            on architectures which support it.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you don't plan to use SELinux
            and/or other security measures.

IRQ subsystem —>

[ ] Expose hardware/virtual IRQ mapping via debugfs

Symbol:     CONFIG_IRQ_DOMAIN_DEBUG

Help:       This option will show the mapping relationship between hardware irq
            numbers and Linux irq numbers. The mapping is exposed via debugfs
            in the file "irq_domain_mapping".
            
            If you don't know what this means you don't need it.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as it's intended for debugging
            purposes.

[ ] Expose irq internals in debugfs

Symbol:     CONFIG_GENERIC_IRQ_DEBUGFS

Help:       Exposes internal state information through debugfs. Mostly for
            developers and debugging of hard to diagnose interrupt problems.

            If you don't know what to do here, say N.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as it's intended for developing
            and debugging purposes.

Timers subsystem —>

Timer tick handling (Periodic timer ticks (constant rate, no dynticks)) —>

(X) Periodic timer ticks (constant rate, no dynticks)

Symbol:     CONFIG_HZ_PERIODIC

Help:       This option keeps the tick running periodically at a constant
            rate, even when the CPU doesn't need it.

Type:       boolean

Choice:     built-in (X)

Reason:     It's highly recommended that you include this option in your kernel
            as it adds a slight performance boost while lowering latency.

            Exclude this option if power saving is one of your concerns.

[ ] Old Idle dynticks config

Symbol:     CONFIG_NO_HZ

Help:       This is the old config entry that enables dynticks idle.
            We keep it around for a little while to enforce backward
            compatibility with older config files.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you've already included
            CONFIG_HZ_PERIODIC.

[ ] High Resolution Timer Support

Symbol:     CONFIG_HIGH_RES_TIMERS

Help:       This option enables high resolution timer support. If your
            hardware is not capable then this option only increases
            the size of the kernel image.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you're sure that no
            application requires it.

            Include this option if power saving is one of your concerns.

CPU/Task time and stats accounting —>

Cputime accounting (Simple tick based cputime accounting) —>

Symbol:     CONFIG_TICK_CPU_ACCOUNTING

Help:       This is the basic tick based cputime accounting that maintains
            statistics about user, system and idle time spent on per jiffies
            granularity.
            
            If unsure, say Y.

Type:       boolean

Choice:     built-in [∗]

Reason:     It's recommended that you include this option as
            CONFIG_VIRT_CPU_ACCOUNTING_GEN is only useful at the moment
            for those who are working on the full dynticks subsystem development.

[ ] Fine granularity task level IRQ time accounting

Symbol:     CONFIG_IRQ_TIME_ACCOUNTING

Help:       Select this option to enable fine granularity task irq time
            accounting. This is done by reading a timestamp on each
            transitions between softirq and hardirq state, so there can be a
            small performance impact.

            If in doubt, say N here.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as it impacts performance.

[ ] BSD Process Accounting

Symbol:     CONFIG_BSD_PROCESS_ACCT

Help:       If you say Y here, a user level program will be able to instruct the
            kernel (via a special system call) to write process accounting
            information to a file: whenever a process exits, information about
            that process will be appended to the file by the kernel.  The
            information includes things such as creation time, owning user,
            command name, memory usage, controlling terminal etc. (the complete
            list is in the struct acct in <file:include/linux/acct.h>).  It is
            up to the user level program to do useful things with this
            information.  This is generally a good idea, so say Y.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option to lower system overhead.

            sys-process/htop might complain, but it's totally harmless.

[ ] Export task/process statistics through netlink

Symbol:     CONFIG_TASKSTATS

Help:       Export selected statistics for tasks/processes through the
            generic netlink interface. Unlike BSD process accounting, the
            statistics are available during the lifetime of tasks/processes as
            responses to commands. Like BSD accounting, they are sent to user
            space on task exit.
            
            Say N if unsure.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option to lower system overhead.

            sys-process/htop might complain, but it's totally harmless.

RCU Subsystem —>

[ ] Make expert-level adjustments to RCU configuration

Symbol:     CONFIG_RCU_EXPERT

Help:       This option needs to be enabled if you wish to make
            expert-level adjustments to RCU configuration.  By default,
            no such adjustments can be made, which has the often-beneficial
            side-effect of preventing "make oldconfig" from asking you all
            sorts of detailed questions about how you would like numerous
            obscure RCU options to be set up.
            
            Say Y if you need to make expert-level adjustments to RCU.
            
            Say N if you are unsure.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as it's mostly for testing
            purposes (especially for larger systems).

            Some of the sub options that show up when including this option
            may help lower latency at the cost of slight system overhead.

< > Kernel .config support

Symbol:     CONFIG_IKCONFIG

Help:       This option enables the complete Linux kernel ".config" file 
            contents to be saved in the kernel. It provides documentation
            of which kernel options are used in a running kernel or in an
            on-disk kernel.  This information can be extracted from the kernel
            image file with the script scripts/extract-ikconfig and used as
            input to rebuild the current kernel or to build another kernel.
            It can also be extracted from a running kernel by reading
            /proc/config.gz if enabled (below).

Type:       tristate

Choice:     excluded < >

Reason:     You can safely exclude this option if you already know what options
            you've enabled in your kernel.

            Instead of including this option, you can backup your kernel's .config
            file and check that file for certain option whenever needed.

(14) Kernel log buffer size (16 => 64KB, 17 => 128KB)

Symbol:     CONFIG_LOG_BUF_SHIFT

Help:       Select the minimal kernel log buffer size as a power of 2.
            The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
            parameter, see below. Any higher size also might be forced
            by "log_buf_len" boot parameter.
            
            Examples:
                       17 => 128 KB
                       16 => 64 KB
                       15 => 32 KB
                       14 => 16 KB
                       13 =>  8 KB
                       12 =>  4 KB

Type:       integer

Choice:     (14) custom

Reason:     You can safely set the value of this option to (14).

            The value (14) is the lowest possible (while staying convenient)
            value that provides good balance between keeping your kernel
            ring buffer from being overwrited constantly while keeping your
            kernel's size to a minimum.
            
            If the output of dmesg is still being truncated (which is highly
            unlikely) then consider increasing the value of this option.

(14) CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)

Symbol:     CONFIG_LOG_CPU_MAX_BUF_SHIFT

Help:       This option allows to increase the default ring buffer size
            according to the number of CPUs. The value defines the contribution
            of each CPU as a power of 2. The used space is typically only few
            lines however it might be much more when problems are reported,
            e.g. backtraces.

            The increased size means that a new buffer has to be allocated and
            the original static one is unused. It makes sense only on systems
            with more CPUs. Therefore this value is used only when the sum of
            contributions is greater than the half of the default kernel ring
            buffer as defined by LOG_BUF_SHIFT. The default values are set
            so that more than 64 CPUs are needed to trigger the allocation.

            Also this option is ignored when "log_buf_len" kernel parameter is
            used as it forces an exact (power of two) size of the ring buffer.
            The number of possible CPUs is used for this computation ignoring
            hotplugging making the computation optimal for the worst case
            scenario while allowing a simple algorithm to be used from bootup.

            Examples shift values and their meaning:
                       17 => 128 KB for each CPU
                       16 =>  64 KB for each CPU
                       15 =>  32 KB for each CPU
                       14 =>  16 KB for each CPU
                       13 =>   8 KB for each CPU
                       12 =>   4 KB for each CPU

Type:       integer

Choice:     (14) custom

Reason:     You can safely set the value of this option to (14).

            The value (14) is the lowest possible (while staying convenient)
            value that provides good balance between keeping your kernel
            ring buffer from being overwrited constantly while keeping your
            kernel's size to a minimum.

            If the output of dmesg is still being truncated (which is highly
            unlikely) then consider increasing the value of this option.

(12) Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)

Symbol:     CONFIG_PRINTK_SAFE_LOG_BUF_SHIFT

Help:       Select the size of an alternate printk per-CPU buffer where messages
            printed from usafe contexts are temporary stored. One example would
            be NMI messages, another one - printk recursion. The messages are
            copied to the main log buffer in a safe context to avoid a deadlock.
            The value defines the size as a power of 2.

            Those messages are rare and limited. The largest one is when
            a backtrace is printed. It usually fits into 4KB. Select
            8KB if you want to be on the safe side.

            Examples:
                       17 => 128 KB for each CPU
                       16 =>  64 KB for each CPU
                       15 =>  32 KB for each CPU
                       14 =>  16 KB for each CPU
                       13 =>   8 KB for each CPU
                       12 =>   4 KB for each CPU

Type:       integer

Choice:     (12) custom

Reason:     You can safely set the value of this option to (12).

            The value (12) is the lowest possible (while staying convenient)
            value that provides good balance between keeping your kernel
            ring buffer from being overwrited constantly while keeping your
            kernel's size to a minimum.

            If the output of dmesg is still being truncated (which is highly
            unlikely) then consider increasing the value of this option.

[ ] Control Group support —>

Symbol:     CONFIG_CGROUPS

Help:       This option adds support for grouping sets of processes together, for
            use with process control subsystems such as Cpusets, CFS, memory
            controls or device isolation.
            See
                  - Documentation/scheduler/sched-design-CFS.txt   (CFS)
                  - Documentation/cgroup-v1/ (features for grouping, isolation
                                            and resource control)

            Say N if unsure.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you're not using Gentoo Linux
            as CGROUPS are considered 'evil' by many users.

            If you're on Gentoo Linux, you'll have to first exclude
            CONFIG_GENTOO_LINUX_PORTAGE.

            Include this option only if your system is reporting a missing
            /sys/fs/cgroup directory.

[ ] Checkpoint/restore support

Symbol:     CONFIG_CHECKPOINT_RESTORE

Help:       Enables additional kernel features in a sake of checkpoint/restore.
            In particular it adds auxiliary prctl codes to setup process text,
            data and heap segment sizes, and a few additional /proc filesystem
            entries.

            If unsure, say N here.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you don't plan on using suspend
            and hibernate.

[ ] Namespaces support —>

Symbol:     CONFIG_NAMESPACES

Help:       Provides the way to make tasks work with different objects using
            the same id. For example same IPC id may refer to different objects
            or same user id or pid may refer to different tasks when used in
            different namespaces.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you're not using Gentoo Linux.

            If you're on Gentoo Linux, some applications may require this option
            and some of the nested options inside it (mainly CONFIG_UTS_NS and
            CONFIG_IPC_NS and sometimes CONFIG_NET_NS for systemd).
            
            Include if you're planning to use LXC (Linux Containers) or if an
            application requires it (and any of the nested options inside it).

[ ] Automatic process group scheduling

Symbol:     CONFIG_SCHED_AUTOGROUP

Help:       This option optimizes the scheduler for common desktop workloads by
            automatically creating and populating task groups.  This separation
            of workloads isolates aggressive CPU burners (like build jobs) from
            desktop applications.  Task group autogeneration is currently based
            upon task session.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you've already excluded
            CONFIG_CGROUPS.

[ ] Enable deprecated sysfs features to support old userspace tools

Symbol:     CONFIG_SYSFS_DEPRECATED

Help:       This option adds code that switches the layout of the "block" class
            devices, to not show up in /sys/class/block/, but only in
            /sys/block/.

            This switch is only active when the sysfs.deprecated=1 boot option is
            passed or the SYSFS_DEPRECATED_V2 option is set.

            This option allows new kernels to run on old distributions and tools,
            which might get confused by /sys/class/block/. Since 2007/2008 all
            major distributions and tools handle this just fine.

            Recent distributions and userspace tools after 2009/2010 depend on
            the existence of /sys/class/block/, and will not work with this
            option enabled.

            Only if you are using a new kernel on an old distribution, you might
            need to say Y here.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you're using a modern up-to-date
            (possibly a rolling-release) distribution.

-∗- Kernel->user space relay support (formerly relayfs)

Symbol:     CONFIG_RELAY

Help:       This option enables support for relay interface support in
            certain file systems (such as debugfs).
            It is designed to provide an efficient mechanism for tools and
            facilities to relay large amounts of data from kernel space to
            user space.
            
            If unsure, say N.

Type:       boolean

Choice:     built-in -∗-

Reason:     It's highly recommended that you include this option in your kernel
            that is if it isn't already forcibly included by CONFIG_PCI,
            CONFIG_DRM_I915, CONFIG_WLAN and a lot of important options. 

[ ] Initial RAM filesystem and RAM disk (initramfs/initrd) support

Symbol:     CONFIG_BLK_DEV_INITRD

Help:       The initial RAM filesystem is a ramfs which is loaded by the
            boot loader (loadlin or lilo) and that is mounted as root
            before the normal boot procedure. It is typically used to
            load modules needed to mount the "real" root file system,
            etc. See <file:Documentation/admin-guide/initrd.rst> for details.

            If RAM disk support (BLK_DEV_RAM) is also included, this
            also enables initial RAM disk (initrd) support and adds
            15 Kbytes (more on some other architectures) to the kernel size.

            If unsure say Y.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you're not using an initrd/initramfs
            to boot your system.

            DOTSLASHLINUX has guides on how to eliminate the need for an initrd/initramfs.
            
            Kindly check this:
            
                https://www.dotslashlinux.com/2017/04/29/booting-the-linux-kernel-without-an-initrd-initramfs/

            and this:
            
                https://www.dotslashlinux.com/2017/04/30/building-intel-cpu-microcode-updates-directly-into-the-linux-kernel/

Compiler optimization level (Optimize for performance) —>

(X) Optimize for performance

Symbol:     CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE

Help:       This is the default optimization level for the kernel, building
            with the "-O2" compiler flag for best performance and most
            helpful compile-time warnings.

Type:       boolean

Choice:     built-in (X)

Reason:     It's highly recommended that you include this option in your kernel
            unless you're extremely space constrained on an embedded system.

[∗] Configure standard kernel features (expert users) —>

Symbol:     CONFIG_EXPERT

Help:       This option allows certain base kernel options and settings
            to be disabled or tweaked. This is for specialized
            environments which can tolerate a "non-standard" kernel.
            Only use this if you really know what you are doing.

Type:       boolean

Choice:     built-in [∗]

Reason:     It's recommended that you include this option in your kernel
            to access its sub menu and exclude some options that won't
            be needed on your system.

[ ] Enable 16-bit UID system calls

Symbol:     CONFIG_UID16

Help:       This option allows certain base kernel options and settings
            to be disabled or tweaked. This is for specialized
            environments which can tolerate a "non-standard" kernel.
            Only use this if you really know what you are doing.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as it was used 12 years ago to
            provide backwards compabtibility for apis using old system calls
            (yes, that's how old this thing is).

[∗] Multiple users, groups and capabilities support

Symbol:     CONFIG_MULTIUSER

Help:       This option enables support for non-root users, groups and
            capabilities.

            If you say N here, all processes will run with UID 0, GID 0, and all
            possible capabilities.  Saying N here also compiles out support for
            system calls related to UIDs, GIDs, and capabilities, such as setuid,
            setgid, and capset.

            If unsure, say Y here.

Type:       boolean

Choice:     built-in [∗]

Reason:     It's highly recommended that you include this option in your kernel
            if you wanted to use a non-root user.

[ ] sgetmask/ssetmask syscalls support

Symbol:     CONFIG_SGETMASK_SYSCALL

Help:       sys_sgetmask and sys_ssetmask are obsolete system calls
            no longer supported in libc but still enabled by default in some
            architectures.

            If unsure, leave the default option here.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as these system calls are obsolete.

[ ] Sysfs syscall support

Symbol:     CONFIG_SYSFS_SYSCALL

Help:       sys_sysfs is an obsolete system call no longer supported in libc.
            Note that disabling this option is more secure but might break
            compatibility with some systems.

            If unsure say Y here.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as this system call is obsolete.

[ ] Sysctl syscall support

Symbol:     CONFIG_SYSCTL_SYSCALL

Help:       sys_sysctl uses binary paths that have been found challenging
            to properly maintain and use.  The interface in /proc/sys
            using paths with ascii names is now the primary path to this
            information.

            Almost nothing using the binary sysctl interface so if you are
            trying to save some space it is probably safe to disable this,
            making your kernel marginally smaller.

            If unsure say N here.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as this system call is obsolete.

[ ] Posix Clocks & timers

Symbol:     CONFIG_POSIX_TIMERS

Help:       This includes native support for POSIX timers to the kernel.
            Some embedded systems have no use for them and therefore they
            can be configured out to reduce the size of the kernel image.

            When this option is disabled, the following syscalls won't be
            available: timer_create, timer_gettime: timer_getoverrun,
            timer_settime, timer_delete, clock_adjtime, getitimer,
            setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
            clock_getres and clock_nanosleep syscalls will be limited to
            CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only.

            If unsure say y.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you're sure that no application
            uses it.

[ ] Load all symbols for debugging/ksymoops

Symbol:     CONFIG_KALLSYMS

Help:       Say Y here to let the kernel print out symbolic crash information and
            symbolic stack backtraces. This increases the size of the kernel
            somewhat, as all symbols have to be loaded into the kernel image.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as it's intended for debugging purposes.

[∗] Enable support for printk

Symbol:     CONFIG_PRINTK

Help:       This option enables normal printk support. Removing it
            eliminates most of the message strings from the kernel image
            and makes the kernel more or less silent. As this makes it
            very difficult to diagnose system problems, saying N here is
            strongly discouraged.

Type:       boolean

Choice:     built-in [∗]

Reason:     It's highly recommended to include this option in your kernel
            to enable dmesg and printk support.

[ ] BUG() support

Symbol:     CONFIG_BUG

Help:       Disabling this option eliminates support for BUG and WARN, reducing
            the size of your kernel image and potentially quietly ignoring
            numerous fatal conditions. You should only consider disabling this
            option for embedded systems with no facilities for reporting errors.
            Just say Y.

Type:       boolean

Choice:     excluded [ ]

Reason:     It's highly recommended that you include this option as it's useful
            for reporting several fatal conditions on your system.

            You can safely exclude this option if you had no need for it.

[∗] Enable PC-Speaker support

Symbol:     CONFIG_PCSPKR_PLATFORM

Help:       This option allows to disable the internal PC-Speaker
            support, saving some memory.

Type:       boolean

Choice:     built-in [∗]

Reason:     You can safely exclude this option if you don't want to hear
            beeps anymore and it won't affect your normal sound experience.

[∗] Enable full-sized data structures for core

Symbol:     CONFIG_BASE_FULL

Help:       Disabling this option reduces the size of miscellaneous core
            kernel data structures. This saves memory on small machines,
            but may reduce performance.

Type:       boolean

Choice:     built-in [∗]

Reason:     It's highly recommended that you include this option in your kernel
            as it adds a slight performance boost.

[∗] Enable futex support

Symbol:     CONFIG_FUTEX

Help:       Disabling this option will cause the kernel to be built without
            support for "fast userspace mutexes".  The resulting kernel may not
            run glibc-based applications correctly.

Type:       boolean

Choice:     built-in [∗]

Reason:     It's highly recommended that you include this option in your kernel
            as it's required by all glibc-based applications.

[∗] Enable eventpoll support[∗]

Symbol:     CONFIG_EPOLL

Help:       Disabling this option will cause the kernel to be built without
            support for epoll family of system calls.

Type:       boolean

Choice:     built-in [∗]

Reason:     It's highly recommended that you include this option in your kernel
            as it's required by CONFIG_GENTOO_LINUX, CONFIG_GENTOO_LINUX_UDEV and
            CONFIG_GENTOO_LINUX_INIT_SYSTEMD.

[∗] Enable signalfd() system call

Symbol:     CONFIG_SIGNALFD

Help:       Enable the signalfd() system call that allows to receive signals
            on a file descriptor.
          
            If unsure, say Y.

Type:       boolean

Choice:     built-in [∗]

Reason:     It's highly recommended that you include this option in your kernel
            as it's required by CONFIG_GENTOO_LINUX, CONFIG_GENTOO_LINUX_UDEV and
            CONFIG_GENTOO_LINUX_INIT_SYSTEMD.

[∗] Enable timerfd() system call

Symbol:     CONFIG_TIMERFD

Help:       Enable the timerfd() system call that allows to receive timer
            events on a file descriptor.

            If unsure, say Y. 

Type:       boolean

Choice:     built-in [∗]

Reason:     It's highly recommended that you include this option in your kernel
            as it's required by CONFIG_GENTOO_LINUX, CONFIG_GENTOO_LINUX_UDEV and
            CONFIG_GENTOO_LINUX_INIT_SYSTEMD.

[∗] Enable eventfd() system call

Symbol:     CONFIG_EVENTFD

Help:       Enable the eventfd() system call that allows to receive both
            kernel notification (ie. KAIO) or userspace notifications.
          
            If unsure, say Y.

Type:       boolean

Choice:     built-in [∗]

Reason:     It's highly recommended that you include this option in your kernel
            as it's required by CONFIG_GENTOO_LINUX, CONFIG_GENTOO_LINUX_UDEV and
            CONFIG_GENTOO_LINUX_INIT_SYSTEMD.

[ ] Enable bpf() system call

Symbol:     CONFIG_BPF_SYSCALL

Help:       Enable the bpf() system call that allows to manipulate eBPF
            programs and maps via file descriptors.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you're not using eBPF programs.

-∗- Use full shmem filesystem

Symbol:     CONFIG_SHMEM

Help:       The shmem is an internal filesystem used to manage shared memory.
            It is backed by swap and manages resource limits. It is also exported
            to userspace as tmpfs if TMPFS is enabled. Disabling this
            option replaces shmem and tmpfs with the much simpler ramfs code,
            which may be appropriate on small systems without swap.

Type:       boolean

Choice:     built-in -∗-

Reason:     It's highly recommended that you include this option in your kernel
            (that is if it isn't already forcibly included by CONFIG_GENTOO_LINUX,
            CONFIG_GENTOO_LINUX_UDEV, DRM_I915 and a lot of important options).

            It's also recommended that you include this option as well if you're using
            a swap partition.

[ ] Enable AIO support

Symbol:     CONFIG_AIO

Help:       This option enables POSIX asynchronous I/O which may by used
            by some high performance threaded applications. Disabling
            this option saves about 7k.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as some users reported that it does
            'bad' things on their respective systems.

[ ] Enable madvise/fadvise syscalls

Symbol:     CONFIG_ADVISE_SYSCALLS

Help:       This option enables the madvise and fadvise syscalls, used by
            applications to advise the kernel about their future memory or file
            usage, improving performance. If building an embedded system where no
            applications use these syscalls, you can disable this option to save
            space.

Type:       boolean

Choice:     excluded [ ]

Reason:     It's highly recommended that you include this option especially if you're
            using www-client/chromium as it's required by chromium's renderer.

            You can safely exclude this option if it isn't required by any of your
            applications.

[ ] Enable userfaultfd() system call

Symbol:     CONFIG_USERFAULTD

Help:       Enable the userfaultfd() system call that allows to intercept and
            handle page faults in userland.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option to lower system overhead.

[ ] Enable PCI quirk workarounds

Symbol:     CONFIG_PCI_QUIRKS

Help:       This enables workarounds for various PCI chipset
            bugs/quirks. Disable this only if your target machine is
            unaffected by PCI quirks.

Type:       boolean

Choice:     built-in [∗]

Reason:     You can safely exclude this option if you're machine is unaffected
            by PCI quirks.

            It's generally a good idea to include this option on systems with a 
            buggy bios.

[ ] Enable membarrier() system call

Symbol:     CONFIG_MEMBARRIER

Help:       Enable the membarrier() system call that allows issuing memory
            barriers across all running threads, which can be used to distribute
            the cost of user-space memory barriers asymmetrically by transforming
            pairs of memory barriers into pairs consisting of membarrier() and a
            compiler barrier.

            If unsure, say Y.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option to lower system overhead.

[ ] Embedded system

Symbol:     CONFIG_EMBEDDED

Help:       This option should be enabled if compiling the kernel for
            an embedded system so certain expert options are available
            for configuration.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you're not building this kernel
            for an embedded system.

[ ] PC/104 support

Symbol:     CONFIG_PC104

Help:       Expose PC/104 form factor device drivers and options available for
            selection and configuration. Enable this option if your target
            machine has a PC/104 bus.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you're not building this kernel
            for an embedded system with a PC/104 bus.

Kernel Performance Events And Counters —>

-∗- Kernel performance events and counters

Symbol:     CONFIG_PERF_EVENTS

Help:       Enable kernel support for various performance events provided
            by software and hardware.

            Software events are supported either built-in or via the
            use of generic tracepoints.

            Most modern CPUs support performance events via performance
            counter registers. These registers count the number of certain
            types of hw events: such as instructions executed, cachemisses
            suffered, or branches mis-predicted - without slowing down the
            kernel or applications. These registers can also trigger interrupts
            when a threshold number of events have passed - and can thus be
            used to profile the code that runs on that CPU.

            The Linux Performance Event subsystem provides an abstraction of
            these software and hardware event capabilities, available via a
            system call and used by the "perf" utility in tools/perf/. It
            provides per task and per CPU counters, and it provides event
            capabilities on top of those.
          
            Say Y if unsure.

Type:       boolean

Choice:     built-in -∗-

Reason:     It's highly recommended that you include this option in your kernel
            (that is if it isn't already forcibly included by CONFIG_X86, CONFIG_NET
            and CONFIG_MULTIUSER).

[ ] Debug: use vmalloc to back perf mmap() buffers

Symbol:     CONFIG_DEBUG_PERF_USE_VMALLOC

Help:       Use vmalloc memory to back perf mmap() buffers.

            Mostly useful for debugging the vmalloc code on platforms
            that don't require it.

            Say N if unsure.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as it's intended for debugging
            purposes.

[ ] Enable VM event counters for /proc/vmstat

Symbol:     CONFIG_VM_EVENT_COUNTERS

Help:       VM event counters are needed for event counts to be shown.
            This option allows the disabling of the VM event counters
            on EXPERT systems.  /proc/vmstat will only show page counts
            if VM event counters are disabled.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option to lower system overhead.

[ ] Enable SLUB debugging support

Symbol:     CONFIG_SLUB_DEBUG

Help:       SLUB has extensive debug support features. Disabling these can
            result in significant savings in code size. This also disables
            SLUB sysfs support. /sys/slab will not exist and there will be
            no support for cache validation etc.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as it's intended for debugging
            purposes.

[∗] Disable heap randomization

Symbol:     CONFIG_COMPAT_BRK

Help:       Randomizing heap placement makes heap exploits harder, but it
            also breaks ancient binaries (including anything libc5 based).
            This option changes the bootup default to heap randomization
            disabled, and can be overridden at runtime by setting
            /proc/sys/kernel/randomize_va_space to 2.

            On non-ancient distros (post-2000 ones) N is usually a safe choice. 

Type:       boolean

Choice:     built-in [∗]

Reason:     You can safely include this option in your kernel to lower system overhead.

Choose SLAB allocator (SLUB (Unqueued Allocator)) —>

(X) SLUB (Unqueued Allocator)

Symbol:     CONFIG_SLUB

Help:       SLUB is a slab allocator that minimizes cache line usage
            instead of managing queues of cached objects (SLAB approach).
            Per cpu caching is realized using slabs of objects instead
            of queues of objects. SLUB can use memory efficiently
            and has enhanced diagnostics. SLUB is the default choice for
            a slab allocator.

Type:       boolean

Choice:     built-in (X)

Reason:     It's highly recommended that you include this option in your kernel
            as CONFIG_SLAB is super old and irrelevant nowadays and CONFIG_SLOB
            is for embedded systems with limited memory and storage space 
            (and will perform really bad when used on a regular desktop/laptop
            as it may take hours to extract a big package).

[ ] SLAB freelist randomization

Symbol:     CONFIG_SLAB_FREELIST_RANDOM

Help:       Randomizes the freelist order used on creating new pages. This
            security feature reduces the predictability of the kernel slab
            allocator against heap overflows.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as it's related to CONFIG_SLAB.

[∗] SLUB per cpu partial cache

Symbol:     CONFIG_SLUB_CPU_PARTIAL

Help:       Per cpu partial caches accellerate objects allocation and freeing
            that is local to a processor at the price of more indeterminism
            in the latency of the free. On overflow these caches will be cleared
            which requires the taking of locks that may cause latency spikes.
            Typically one would choose no for a realtime system.

Type:       boolean

Choice:     built-in [∗]

Reason:     It's recommended that you include this option as it adds a performance
            boost and speeds up object allocation and freeing at the cost of a 
            slight increase in memory footprint.

            Exclude only if you're concerned about latency.

[ ] Profiling support

Symbol:     CONFIG_PROFILING

Help:       Say Y here to enable the extended profiling support mechanisms used
            by profilers such as OProfile.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option to lower system overhead.

[ ] Kprobes

Symbol:     CONFIG_KPROBES

Help:       Kprobes allows you to trap at almost any kernel address and
            execute a callback function.  register_kprobe() establishes
            a probepoint and specifies the callback.  Kprobes is useful
            for kernel debugging, non-intrusive instrumentation and testing.
            If in doubt, say "N".

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option to lower system overhead.

[ ] Optimize very unlikely/likely branches

Symbol:     CONFIG_JUMP_LABEL

Help:       This option enables a transparent branch optimization that
            makes certain almost-always-true or almost-always-false branch
            conditions even cheaper to execute within the kernel.

            Certain performance-sensitive kernel code, such as trace points,
            scheduler functionality, networking code and KVM have such
            branches and include support for this optimization technique.

            If it is detected that the compiler has support for "asm goto",
            the kernel will compile such branches with just a nop
            instruction. When the condition flag is toggled to true, the
            nop will be converted to a jump instruction to execute the
            conditional block of instructions.

            This technique lowers overhead and stress on the branch prediction
            of the processor and generally makes the kernel faster. The update
            of the condition is slower, but those are always very rare.

            ( On 32-bit x86, the necessary options added to the compiler
              flags may increase the size of the kernel slightly. )

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as it's intended for debugging
            purposes.

[ ] GCC plugins —-

Symbol:     CONFIG_GCC_PLUGINS

Help:       GCC plugins are loadable modules that provide extra features to the
            compiler. They are useful for runtime instrumentation and static analysis.

            See Documentation/gcc-plugins.txt for details.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option as you probably won't need those extra
            modules provided.

Stack Protector buffer overflow detection (None) —>

Symbol:     CONFIG_CC_STACKPROTECTOR_NONE

Help:       Disable "stack-protector" GCC feature.

Type:       boolean

Choice:     built-in [∗]

Reason:     You can safely exclude this option to lower system overhead.

(28) Number of bits to use for ASLR of mmap base address

Symbol:     CONFIG_ARCH_MMAP_RND_BITS

Help:       This value can be used to select the number of bits to use to
            determine the random offset to the base address of vma regions
            resulting from mmap allocations. This value will be bounded
            by the architecture's minimum and maximum supported values.

            This value can be changed after boot using the
            /proc/sys/vm/mmap_rnd_bits tunable 

Type:       integer

Choice:     (28) default

Reason:     You can safely leave the value of this option to its default value
            of (28).

(8) Number of bits to use for ASLR of mmap base address for compatible applications

Symbol:     CONFIG_ARCH_MMAP_RND_COMPAT_BITS

Help:       This value can be used to select the number of bits to use to
            determine the random offset to the base address of vma regions
            resulting from mmap allocations for compatible applications This
            value will be bounded by the architecture's minimum and maximum
            supported values.

            This value can be changed after boot using the
            /proc/sys/vm/mmap_rnd_compat_bits tunable

Type:       integer

Choice:     (8) default

Reason:     You can safely leave the value of this option to its default value
            of (8).

[ ] Use a virtually-mapped stack

Symbol:     CONFIG_VMAP_STACK

Help:       Enable this if you want the use virtually-mapped kernel stacks
            with guard pages.  This causes kernel stack overflows to be
            caught immediately rather than causing difficult-to-diagnose
            corruption.

            This is presently incompatible with KASAN because KASAN expects
            the stack to map directly to the KASAN shadow map using a formula
            that is incorrect if the stack is in vmalloc space.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option to lower system overhead.

[ ] Perform full reference count validation at the expense of speed

Symbol:     CONFIG_REFCOUNT_FULL

Help:       Enabling this switches the refcounting infrastructure from a fast
            unchecked atomic_t implementation to a fully state checked
            implementation, which can be (slightly) slower but provides protections
            against various use-after-free conditions that can be used in
            security flaw exploits.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option to lower system overhead.

GCOV-based kernel profiling —>

[ ] Enable gcov-based kernel profiling

Symbol:     CONFIG_GCOV_KERNEL

Help:       This option enables gcov-based code profiling (e.g. for code coverage
            measurements).

            If unsure, say N.

            Additionally specify CONFIG_GCOV_PROFILE_ALL=y to get profiling data
            for the entire kernel. To enable profiling for specific files or
            directories, add a line similar to the following to the respective
            Makefile:

            For a single file (e.g. main.o):
                    GCOV_PROFILE_main.o := y

            For all files in one directory:
                    GCOV_PROFILE := y

            To exclude files from being profiled even when CONFIG_GCOV_PROFILE_ALL
            is specified, use:

                    GCOV_PROFILE_main.o := n
            and:
                    GCOV_PROFILE := n

            Note that the debugfs filesystem has to be mounted to access
            profiling data.

Type:       boolean

Choice:     excluded [ ]

Reason:     You can safely exclude this option if you've already excluded
            CONFIG_PROFILING to lower system overhead.

---

Chinese Translation

One of DOTSLASHLINUX followers 杨鑫 (Yang Mame) from China, decided to follow up with the series and provide Chinese translation of the kernel configuration guides on his blog.

To read this guide in Chinese click here.