Boot messages Explained Kernel Messages

This entry was posted by Tuesday, 7 April, 2009
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Most users when inserting a new Linux CD can be somewhat paniced by the verbose text that the kernel spits out. Some distros have a flash screen which hide this and others just let loose.
Dont fret! its only debug so you know whats happening!
After a while using Linux you will be able to understand a bit about what it means or is saying.

The Linux kernel is the central interface between the user and the hardware. As such, it has to incorporate support for hardware if you are to use it. Often, though, cryptic device names are used by the system, making it difficult at first inspection to determine if some particular hardware is supported. The command ‘dmesg’, which is used to print kernel messages, is very useful in determining if a piece of hardware has been found, and if so, what the system is referring to it as.

Kernel output on an i386 system

Shown below is a dmesg from an x86 system immediately after boot. The output is indented by several space, and comments and descriptions are left justified.

    Linux version 2.2.14-5.0 (root@porky.devel.redhat.com) (gcc version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)) #1 Tue Mar 7 20:53:41 EST 2000

First up is the kernel version (2.2.14) and build (5), along with who built it, with what compile it was built, and when it wass built. This can be some inportant information, as some kernel versions and the GCC project don’t interact correctly.

    Detected 300683434 Hz processor.

My K6/2-300 processor running at 300 MHz.

    Console: colour VGA+ 80x25

A standard PC console screen (15 inch monitor).

    Calibrating delay loop... 599.65 BogoMIPS

The useless benchmark of BogoMIPS. They’re bogus (hence the name), but are often used as a relative processor speed indicator.

    Memory: 63008k/65536k available (1084k kernel code, 412k reserved, 968k data, 64k init, 0k bigmem)

My memory statistics. My machine has 64MB of real memory.

    Dentry hash table entries: 262144 (order 9, 2048k)

The dentry cache (dcache) represents the kernel’s view of the namespace of mounted filesystems. There’s pretty good documentation of it in Documentation/filesystems/vfs.txt in the kernel source tree.

    Buffer cache hash table entries: 65536 (order 6, 256k)

In 2.2, the buffer cache is used for caching and aggregating data for writes to block devices. After 2.3.6, it is used for caching fs metadata, such as inode information.

    Page cache hash table entries: 16384 (order 4, 64k)

In 2.2, the page (VM) cache is used for caching swap, read and mmap data (which was bad, because shared writable mappings were ugly). After 2.3.6, it also is used for write data (i.e., the buffer and page caches are mostly unified), and all became happiness and light (sorta like BSD).

    VFS: Diskquotas version dquot_6.4.0 initialized

My kernel support quotas (though I’m not using them).

    CPU: AMD AMD-K6(tm) 3D processor stepping 00

A quick identification of the processor.

    Checking 386/387 coupling... OK, FPU using exception 16 error reporting.
    Checking 'hlt' instruction... OK.

I seem to recall there being some Intel processor issues, which the kernel has to know about if it’s to invoke corrections.

    POSIX conformance testing by UNIFIX
    PCI: PCI BIOS revision 2.10 entry at 0xfb490

And we start the probing of the PCI bus for peripherals.

    PCI: Using configuration type 1
    PCI: Probing PCI hardware
    PCI: 00:38 [1106/0586]: Work around ISA DMA hangs (00)
    Activating ISA DMA hang workarounds.
    Linux NET4.0 for Linux 2.2

This kernel supports the Net4 networking codebase, which has a lot of features yet to be fully utilized.

    Based upon Swansea University Computer Society NET3.039
    NET4: Unix domain sockets 1.0 for Linux NET4.0.
    NET4: Linux TCP/IP 1.0 for NET4.0
    IP Protocols: ICMP, UDP, TCP, IGMP

My core IP protocols supported. While not needed, IGMP can be fun. Note that some networks do not support muticasting.

    TCP: Hash tables configured (ehash 65536 bhash 65536)
    Initializing RT netlink socket
    Starting kswapd v 1.5
    Detected PS/2 Mouse Port.

Should be quite obvious…

    Serial driver version 4.27 with MANY_PORTS MULTIPORT SHARE_IRQ enabled
    ttyS00 at 0x03f8 (irq = 4) is a 16550A
    ttyS01 at 0x02f8 (irq = 3) is a 16550A

The information about my serial ports.

    pty: 256 Unix98 ptys configured
    apm: BIOS version 1.2 Flags 0x07 (Driver version 1.9)

My motherboard supports the APM standard for sleeping.

    Real Time Clock Driver v1.09
    RAM disk driver initialized: 16 RAM disks of 4096K size

My kernel supports RAM disks. While I’m not using any most days, sometimes I do use them; if you have the memory, they make a real fast filesystem (like /tmp or, for a webserver, the main pages loaded).

    VP_IDE: IDE controller on PCI bus 00 dev 39
    VP_IDE: not 100% native mode: will probe irqs later
    ide0: BM-DMA at 0xe000-0xe007, BIOS settings: hda:DMA, hdb:DMA
    ide1: BM-DMA at 0xe008-0xe00f, BIOS settings: hdc:DMA, hdd:DMA

My IDE controllers.

    hda: Maxtor 51369U3, ATA DISK drive

My hard drive in the machine.

    hdb: IDE/ATAPI CD-ROM 32X, ATAPI CDROM drive

My CDROM drive.

    ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
    hda: Maxtor 51369U3, 12949MB w/2048kB Cache, CHS=6577/64/63
    hdb: ATAPI 16X CD-ROM drive, 128kB Cache

Disk information.

    Uniform CDROM driver Revision: 2.56
    Floppy drive(s): fd0 is 1.44M
    FDC 0 is a post-1991 82077

Floppy drive information.

    md driver 0.90.0 MAX_MD_DEVS=256, MAX_REAL=12
    raid5: measuring checksumming speed
    raid5: MMX detected, trying high-speed MMX checksum routines
    pII_mmx : 761.238 MB/sec
    p5_mmx : 726.567 MB/sec
    8regs : 447.675 MB/sec
    32regs : 308.610 MB/sec
    using fastest function: pII_mmx (761.238 MB/sec)

A bunch of RAID and MD (used in multiple device devices, like disk arrays) information, again not used.

    scsi : 0 hosts.
    scsi : detected total.

While the kernel supports SCSI, I’m not using any on this host.

    md.c: sizeof(mdp_super_t) = 4096
    Partition check:
    hda: hda1 hda2 < hda5 hda6 >

My disk partition information. The brackets indicate extended partitions.

    autodetecting RAID arrays
    autorun ...
    ... autorun DONE.

Like I said above, I’m using not using any RAID arrays.

    VFS: Mounted root (ext2 filesystem) readonly.

At this point we’re almost done with the kernel and ready to start the system.

    Freeing unused kernel memory: 64k freed
    Adding Swap: 66488k swap-space (priority -1)
    ne2k-pci.c:vpre-1.00e 5/27/99 D. Becker/P. Gortmaker http://cesdis.gsfc.nasa.gov/linux/drivers/ne2k-pci.html
    ne2k-pci.c: PCI NE2000 clone 'RealTek RTL-8029' at I/O 0xe800, IRQ 11.
    eth0: RealTek RTL-8029 found at 0xe800, IRQ 11, 00:80:AD:41:22:10.

My ethernet device is a PCI NE2000 based device. (A real cheap NIC, but almost every OS supports it.)

    VFS: Disk change detected on device fd(2,0)

At this point, the kernel is done booting and we’re ready to start /sbin/init (unless we supplied some information about init upon boot). The system then starts rc.sysinit and begins normal boot operations. The kernel has finished booting.

Last-Modified: 2007-03-07 19:38:50

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