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By reading the note 1538626.1 from MOS Meta Link, I know that we should use udev to change the ownership of some device for the further installation of oracle real application cluster: I met a lot of similar udev rules for the purpose of changing the owner of asm disk in internet as follow:

ENV{DM_NAME}=="data01", OWNER:="oragrid", GROUP:="asmadmin", MODE:="660", SYMLINK+="iscsi/asm-$env{DM_NAME}"
ENV{DM_NAME}=="data02", OWNER:="oragrid", GROUP:="asmadmin", MODE:="660", SYMLINK+="iscsi/asm-$env{DM_NAME}"
ENV{DM_NAME}=="data03", OWNER:="oragrid", GROUP:="asmadmin", MODE:="660", SYMLINK+="iscsi/asm-$env{DM_NAME}"
ENV{DM_NAME}=="data04", OWNER:="oragrid", GROUP:="asmadmin", MODE:="660", SYMLINK+="iscsi/asm-$env{DM_NAME}"
ENV{DM_NAME}=="crs01", OWNER:="oragrid", GROUP:="asmadmin", MODE:="660", SYMLINK+="iscsi/asm-$env{DM_NAME}"
ENV{DM_NAME}=="crs02", OWNER:="oragrid", GROUP:="asmadmin", MODE:="660", SYMLINK+="iscsi/asm-$env{DM_NAME}"
ENV{DM_NAME}=="crs03", OWNER:="oragrid", GROUP:="asmadmin", MODE:="660", SYMLINK+="iscsi/asm-$env{DM_NAME}"

After the rules is defined, we can restart the udev and get the device with ownership changed

#ls -l /dev/dm*
brw-rw---- 1 root    disk     253,  0 Dec 15 14:18 /dev/dm-0
brw-rw---- 1 root    disk     253,  1 Dec 15 14:18 /dev/dm-1
brw-rw---- 1 root    disk     253, 10 Dec 15 14:18 /dev/dm-10
brw-rw---- 1 oragrid asmadmin 253,  2 Dec 15 14:18 /dev/dm-2
brw-rw---- 1 oragrid asmadmin 253,  3 Dec 15 14:18 /dev/dm-3
brw-rw---- 1 oragrid asmadmin 253,  4 Dec 15 14:18 /dev/dm-4
brw-rw---- 1 oragrid asmadmin 253,  5 Dec 15 14:18 /dev/dm-5
brw-rw---- 1 oragrid asmadmin 253,  7 Dec 15 14:18 /dev/dm-7
brw-rw---- 1 oragrid asmadmin 253,  8 Dec 15 14:18 /dev/dm-8
brw-rw---- 1 oragrid asmadmin 253,  9 Dec 15 14:18 /dev/dm-9

At the same time, because we use the key SYMLINK in the udev rules, we can get the symbolic links which act as alternative names for the device node

#  ls -l /dev/iscsi/*
lrwxrwxrwx 1 root root 7 Dec 15 14:18 /dev/asm/asm-crs01 -> ../dm-5
lrwxrwxrwx 1 root root 7 Dec 15 14:18 /dev/asm/asm-crs02 -> ../dm-7
lrwxrwxrwx 1 root root 7 Dec 15 14:18 /dev/asm/asm-crs03 -> ../dm-8
lrwxrwxrwx 1 root root 7 Dec 15 14:18 /dev/asm/asm-data01 -> ../dm-9
lrwxrwxrwx 1 root root 7 Dec 15 14:18 /dev/asm/asm-data02 -> ../dm-2
lrwxrwxrwx 1 root root 7 Dec 15 14:18 /dev/asm/asm-data03 -> ../dm-3
lrwxrwxrwx 1 root root 7 Dec 15 14:18 /dev/asm/asm-data04 -> ../dm-4

It seems that such SYMLINK has no relationship with the rac installation, why is the purpose of adding the sysmlink property in the udev rules?Can I get rid of sysmlink in the udev rules?

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It is not mandatory, do not use it if you do not want to.

Creating such symlinks just makes it easier to distinguish the ASM disks. You can even set asm_diskstring to /dev/iscsi/* with the above.

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