17 modifying kernel module behavior through modprobe

By OK -
show which modules are loaded

[svn@svn ~]$ lsmod
Module                  Size  Used by
nls_utf8               12557  1
isofs                  39844  1
fuse                   87741  3
binfmt_misc            17468  1
xt_CHECKSUM            12549  1
ipt_MASQUERADE         12678  3
nf_nat_masquerade_ipv4    13412  1 ipt_MASQUERADE
tun                    27226  1


[svn@svn ~]$ lsmod | grep e100
e1000                 137544  0

show info of particular module

[svn@svn ~]$ modinfo e1000
filename:       /lib/modules/3.10.0-514.el7.x86_64/kernel/drivers/net/ethernet/intel/e1000/e1000.ko
version:        7.3.21-k8-NAPI
license:        GPL
description:    Intel(R) PRO/1000 Network Driver
author:         Intel Corporation, <linux.nics@intel.com>
rhelversion:    7.3
...
...
...
parm:           TxDescriptors:Number of transmit descriptors (array of int)
parm:           RxDescriptors:Number of receive descriptors (array of int)
parm:           Speed:Speed setting (array of int)
parm:           Duplex:Duplex setting (array of int)
parm:           AutoNeg:Advertised auto-negotiation setting (array of int)

===================
we cannot modify parameters of loaded module

[svn@svn ~]$ modprobe -r cdrom
modprobe: FATAL: Module cdrom is in use.

[svn@svn ~]$ modinfo cdrom
filename:       /lib/modules/3.10.0-514.el7.x86_64/kernel/drivers/cdrom/cdrom.ko
license:        GPL
rhelversion:    7.3
srcversion:     BE3BD0D17D080229D55B173
depends:      
intree:         Y
vermagic:       3.10.0-514.el7.x86_64 SMP mod_unload modversions
signer:         CentOS Linux kernel signing key
sig_key:        D4:88:63:A7:C1:6F:CC:27:41:23:E6:29:8F:74:F0:57:AF:19:FC:54
sig_hashalgo:   sha256
parm:           debug:bool
parm:           autoclose:bool
parm:           autoeject:bool
parm:           lockdoor:bool
parm:           check_media_type:bool
parm:           mrw_format_restart:bool
[svn@svn ~]$
=======================
on older linux version to modify parameters there was a file
/etc/modprobe.conf
in RHEL 7 this is no longer the case

[svn@svn modprobe.d]$ man 5 modprobe.d

in order to change parameter we created a file
[svn@svn modprobe.d]$ cat cdrom.conf 
options cdrom lockdoor=0

the only option to verify the module is to reboot

some parameters values are presented in
[svn@svn modprobe.d]$ ls /sys/module/
8250                 ip6_tables              ppdev
ablk_helper          ip6table_security       printk
ac97_bus             ip6t_REJECT             processor
acpi                 ip6t_rpfilter           psmouse
acpiphp              ip_set                  pstore
aesni_intel          iptable_filter          random
ata_generic          iptable_mangle          rcupdate
ata_piix             iptable_nat             rcutree
auth_rpcgss          iptable_raw             rng_core
battery              ip_tables               scsi_dh_alua

[svn@svn modprobe.d]$ dmesg | grep -P5 cdrom
[    3.189840] [drm] Initialized vmwgfx 2.10.0 20160210 for 0000:00:0f.0 on minor 0
[    3.224905] ata2.00: ATAPI: VMware Virtual IDE CDROM Drive, 00000001, max UDMA/33
[    3.230845] ata2.00: configured for UDMA/33
[    3.232809] scsi 2:0:0:0: CD-ROM            NECVMWar VMware IDE CDR10 1.00 PQ: 0 ANSI: 5
[    3.267043] sr 2:0:0:0: [sr0] scsi3-mmc drive: 1x/1x writer dvd-ram cd/rw xa/form2 cdda tray
[    3.267050] cdrom: Uniform CD-ROM driver Revision: 3.20
[    3.267339] sr 2:0:0:0: Attached scsi CD-ROM sr0
[    3.582770] e1000 0000:02:01.0 eth0: (PCI:66MHz:32-bit) 00:0c:29:e7:8e:ec
[    3.582787] e1000 0000:02:01.0 eth0: Intel(R) PRO/1000 Network Connection
[    3.783944] SGI XFS with ACLs, security attributes, no debug enabled
[    3.786122] XFS (dm-0): Mounting V5 Filesystem
[svn@svn modprobe.d]$ 


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