Most of the advanced Linux users like to custom compile their own kernels so that they can remove all the fat (non-essential stuff) that by default is compiled or built as modules into the stock kernel from Linux distribution vendor. For example, if you install Debian Lenny (5.0) which comes with 2.6.26 kernel, you will see that almost everything is compiled either into the kernel or built as modules thus unnecessary increasing the size of the kernel.

So suppose you decide to compile/build your own custom kernel by only including the device drivers that are required by your hardware device on your system/computer. Now the problem is that how do you know which drivers are being used by which devices, so that you can only include them in your custom kernel.

There are two ways to do this:

Method 1: lspci

“lspci” is a very powerful utility to get device information from your system. To install lspci do the following:

# apt-get update
# apt-get install pciutils

Now give the following command:
# lspci -k

Output:
00:00.0 RAM memory: nVidia Corporation MCP61 Memory Controller (rev a1)
00:01.0 ISA bridge: nVidia Corporation MCP61 LPC Bridge (rev a2)
00:01.1 SMBus: nVidia Corporation MCP61 SMBus (rev a2)
Kernel driver in use: nForce2_smbus
Kernel modules: i2c-nforce2
00:01.2 RAM memory: nVidia Corporation MCP61 Memory Controller (rev a2)
00:02.0 USB Controller: nVidia Corporation MCP61 USB Controller (rev a3)
Kernel driver in use: ohci_hcd
Kernel modules: ohci-hcd
00:02.1 USB Controller: nVidia Corporation MCP61 USB Controller (rev a3)
Kernel driver in use: ehci_hcd
Kernel modules: ehci-hcd
00:04.0 PCI bridge: nVidia Corporation MCP61 PCI bridge (rev a1)
00:05.0 Audio device: nVidia Corporation MCP61 High Definition Audio (rev a2)
Kernel driver in use: HDA Intel
Kernel modules: snd-hda-intel
00:06.0 IDE interface: nVidia Corporation MCP61 IDE (rev a2)
Kernel driver in use: AMD_IDE
Kernel modules: amd74xx, ide-pci-generic, ata_generic
00:07.0 Bridge: nVidia Corporation MCP61 Ethernet (rev a2)
Kernel driver in use: forcedeth
Kernel modules: forcedeth
00:08.0 IDE interface: nVidia Corporation MCP61 SATA Controller (rev a2)
Kernel driver in use: sata_nv
Kernel modules: ide-pci-generic, sata_nv, ata_generic
00:09.0 PCI bridge: nVidia Corporation MCP61 PCI Express bridge (rev a2)
Kernel driver in use: pcieport-driver
Kernel modules: shpchp
00:18.0 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] HyperTransport Technology Configuration
00:18.1 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] Address Map
00:18.2 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] DRAM Controller
00:18.3 Host bridge: Advanced Micro Devices [AMD] K8 [Athlon64/Opteron] Miscellaneous Control
Kernel driver in use: k8temp
Kernel modules: k8temp
02:00.0 VGA compatible controller: nVidia Corporation GeForce 8500 GT (rev a1)
Kernel modules: nvidiafb

Now the above output is very useful because it first shows you all the PCI devices attached to your system and then tells you what kernel modules (device drivers), shown in green color,  are being used by them.

Method 2: lsmod

Give the command:
# lsmod

Output:
Module                  Size  Used by
binfmt_misc            13580  1
nfsd                  248360  13
lockd                  68560  1 nfsd
nfs_acl                 7552  1 nfsd
auth_rpcgss            47520  1 nfsd
sunrpc                197480  11 nfsd,lockd,nfs_acl,auth_rpcgss
exportfs                8704  1 nfsd
ppdev                  11656  0
lp                     14724  0
autofs4                24200  0
ipv6                  288328  51
battery                16904  0
powernow_k8            17156  1
cpufreq_userspace       8452  0
cpufreq_conservative    11784  0
cpufreq_stats           9120  0
cpufreq_powersave       6400  0
cpufreq_ondemand       11792  1
freq_table              9344  3 powernow_k8,cpufreq_stats,cpufreq_ondemand
fuse                   53184  1
it87                   28952  0
hwmon_vid               7296  1 it87
loop                   19468  0
snd_hda_intel         434904  0
snd_pcm_oss            41760  0
snd_mixer_oss          18816  1 snd_pcm_oss
snd_pcm                81672  2 snd_hda_intel,snd_pcm_oss
snd_seq_dummy           7428  0
snd_seq_oss            33152  0
snd_seq_midi           11072  0
snd_rawmidi            26784  1 snd_seq_midi
snd_seq_midi_event     11904  2 snd_seq_oss,snd_seq_midi
snd_seq                54304  6 snd_seq_dummy,snd_seq_oss,snd_seq_midi,snd_seq_midi_event
snd_timer              25744  2 snd_pcm,snd_seq
snd_seq_device         11668  5 snd_seq_dummy,snd_seq_oss,snd_seq_midi,snd_rawmidi,snd_seq
snd                    63688  9 snd_hda_intel,snd_pcm_oss,snd_mixer_oss,snd_pcm,snd_seq_oss,snd_rawmidi,snd_seq,snd_timer,snd_seq_device
parport_pc             31016  1
parport                41776  3 ppdev,lp,parport_pc
soundcore              12064  1 snd
snd_page_alloc         13072  2 snd_hda_intel,snd_pcm
k8temp                  9216  0
button                 11680  0
i2c_nforce2            10752  0
i2c_core               27936  1 i2c_nforce2
evdev                  14208  3
ext3                  125072  3
jbd                    51240  1 ext3
mbcache                12804  1 ext3
sg                     36448  0
sr_mod                 19652  0
sd_mod                 29376  3
cdrom                  37928  1 sr_mod
ide_disk               16512  3
usb_storage            94528  0
ata_generic            10116  0
sata_nv                27528  3
libata                165472  2 ata_generic,sata_nv
scsi_mod              160760  5 sg,sr_mod,sd_mod,usb_storage,libata
dock                   14112  1 libata
floppy                 61672  0
ide_pci_generic         9220  0 [permanent]
forcedeth              54032  0
amd74xx                13448  0 [permanent]
ide_core              128284  3 ide_disk,ide_pci_generic,amd74xx
ehci_hcd               36108  0
ohci_hcd               25092  0
thermal                22688  0
processor              42304  2 powernow_k8,thermal
fan                     9352  0
thermal_sys            17728  3 thermal,processor,fan

The above command gives you a comprehensive list of all the Linux kernel modules (essential and optional) that are being currently used by your system.

Now you can easily search by the modules names (shown in green in Method1 or the ones listed in Method 2) when you do your make xconfig or make menuconfig to compile a custom Linux kernel.

To search in:
make xconfig - Edit->Find or Ctrl+F
make menuconfig - Press "/" key

That’s it. You can now simply decide to either include the above drivers into the kernel (Y) or you can include them as modules (M) and can produce a lean and mean kernel.

Note: Of course you will need to include some additional modules which are not listed as a part of lspci above like filesystem modules (like Ext3, Ext2, etc).If you don’t include a filesystem module then chances are your kernel will fail to boot. However Method 2 will list those (see ext3 in the Method 2 output) and you can include them in your kernel.

Happy compiling!

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