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Full Discussion: /dev/null not writable
Operating Systems Solaris /dev/null not writable Post 302537968 by bin-doph on Monday 11th of July 2011 09:04:43 AM
Old 07-11-2011
Hi everybody,

thanks for all the answers. I did try to chmod the device from the zone and from the global zone, almost without success. However, today I discovered that chmoding did work, but not for very long.

Code:
bash-3.00# chmod go+w /dev/null; ls -lah /dev/null
crw-rw-rw-   1 root     sys       13,  2 Jul 11 15:01 /dev/null
bash-3.00# ls -lah /dev/null
crw-r--r--   1 root     sys       13,  2 Jul 11 15:01 /dev/null

Between those two commands is a time-delta of me pasting the second command into the shell. I've tried to figure out what process does the permission-changes on the device, but so far without success. I hardly doubt there is a custom-script with the purpose of chmoding /dev/null, at least as far as I know...
 

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LEARN ABOUT CENTOS

ports

ports(1M)						  System Administration Commands						 ports(1M)

NAME

       ports - creates /dev entries and inittab entries for serial lines

SYNOPSIS

       /usr/sbin/ports [-r rootdir]

DESCRIPTION

       devfsadm(1M) is now the preferred command for /dev and /devices and should be used instead of ports.

       The  ports  command  creates symbolic links in the /dev/term and /dev/cua directories to the serial-port character device files in /devices
       and adds new entries in /etc/inittab for non-system ports found.  System-board ports are given single lower-case letters for names (such as
       a and b) while other ports are named numerically.

       ports  searches the kernel device tree to find the serial devices attached to the system. It also checks /dev/term and /dev/cua to see what
       symbolic links to serial devices already exist. ports then performs the following:

       1.  Assigns new numbers (or letters for system-board ports) to ports that are attached to the system but do not have /dev/term and /dev/cua
	   entries. The numbers or letters assigned are the lowest-unused numbers or letters.

       2.  Removes dangling links: links from /dev/term and /dev/cua pointing to no-longer-existing ports.

       3.  Creates new /dev/term and /dev/cua links for new serial devices.

       4.  Invokes sacadm(1M) to make new port monitor entries for the new devices. This is not done automatically for on-board ports; on worksta-
	   tions these ports are often not used for dial-in sessions, so a port-monitor for one of these ports must be created explicitly.

       If the configuration has not changed, ports exits without doing anything.

   Notice to Driver Writers
       ports considers devices with a node type of DDI_NT_SERIAL, DDI_NT_SERIAL_MB, DDI_NT_SERIAL_DO, or DDI_NT_SERIAL_MB_DO  to  be  serial  port
       devices.  Devices  with	one  of  these node types must create minor device names that obey the following conventions when calling ddi_cre-
       ate_minor_node(9F).

	 o  The minor name for non-system port devices (DDI_NT_SERIAL) consists of an ASCII numeric string, where the first port on the device	is
	    named 0, the second named 1, the third named 2, up to the number of ports provided by the device.

	 o  The  minor	name for non-system dialout devices (DDI_NT_SERIAL_DO) is the ASCII numeric port name, concatenated with ,cu. For example,
	    the minor name for the first dialout port on the serial board is 0,cu.

	 o  The minor name for system-board port devices (DDI_NT_SERIAL_MB) consists of a string containing a single  ASCII  lowercase	character,
	    where the first port on the device is named a, the second is named b, the third is named c, for all ports on the device (or up through
	    port z).

	 o  The minor name for system-board dialout devices (DDI_NT_SERIAL_MB_DO) consists of the lowercase character port name, concatenated with
	    ,cu. For example, the minor name for the first dialout port on the on-board serial device is a,cu.

       To  prevent  disks  from attempting to automatically generate links for a device, drivers must specify a private node type and refrain from
       using one of the above node types when calling ddi_create_minor_node(9F).

OPTIONS

       The following options are supported:

       -r rootdir      Causes ports to presume that the /dev/term, /dev/cua, and /devices directories are found under rootdir, not directly  under
		       /. If this argument is specified, sacadm(1M) is not invoked, since it would update terminal administration files under /etc
		       without regard to the rootdir.

EXAMPLES

       Example 1: Creating the Serial and Dialout Minor Device Nodes

       The following example creates the serial and dialout minor device nodes from the xkserial driver's attach(9E) function:

       /*
       * Create the minor number by combining the instance number
       * with the port number.
       */ #define XKNUMPORTS	       8
       #define XKMINORNUM(i, p)     ((i) << 4 | (p))
       #define XKMINORNUM_DO(i, p)  ((i) << 4 | (p) | 0x80)
       int
       xkserialattach(dev_info_t *dip, ddi_attach_cmd_t cmd)
       {
	  int instance, portnum;
	  char name[8];
	      /* other stuff in attach... */
	  instance = ddi_get_instance(dip);
	  for (portnum = 0; portnum < XKNUMPORTS; portnum++) {
	      /*
	       * create the serial port device
	       */
	       sprintf(name, "%d", portnum);
	       ddi_create_minor_node(dip, name, S_IFCHR,
		  XKMINORNUM(instance, portnum), DDI_NT_SERIAL, 0);

	       /*
		* create the dialout device
		*/
		sprintf(name,"%d,cu", portnum);
		ddi_create_minor_node(dip, name, S_IFCHR,
		    XKMINORNUM_DO(instance, portnum), DDI_NT_SERIAL_DO, 0);
	    }
       }

       Example 2: Installing the xkserial Port Driver on a Sun Fire 4800

       The following example installs the xkserial port driver on a Sun Fire 4800 (with the driver  controlling  the  fictional  XKSerial  8  port
       serial board), with these special files in /devices:

       # ls -l /devices/ssm@0,0/pci@18,700000/pci@1/xkserial@f,800000/
       crw-r-----   1 root sys	 32,  16 Aug 29 00:02 xkserial@2000:0
       crw-r-----   1 root sys	 32, 144 Aug 29 00:02 xkserial@2000:0,cu
       crw-r-----   1 root sys	 32,  17 Aug 29 00:02 xkserial@2000:1
       crw-r-----   1 root sys	 32, 145 Aug 29 00:02 xkserial@2000:1,cu
       crw-r-----   1 root sys	 32,  18 Aug 29 00:02 xkserial@2000:2
       crw-r-----   1 root sys	 32, 146 Aug 29 00:02 xkserial@2000:2,cu
       crw-r-----   1 root sys	 32,  19 Aug 29 00:02 xkserial@2000:3
       crw-r-----   1 root sys	 32, 147 Aug 29 00:02 xkserial@2000:3,cu
       crw-r-----   1 root sys	 32,  20 Aug 29 00:02 xkserial@2000:4
       crw-r-----   1 root sys	 32, 148 Aug 29 00:02 xkserial@2000:4,cu
       crw-r-----   1 root sys	 32,  21 Aug 29 00:02 xkserial@2000:5
       crw-r-----   1 root sys	 32, 149 Aug 29 00:02 xkserial@2000:5,cu
       crw-r-----   1 root sys	 32,  22 Aug 29 00:02 xkserial@2000:6
       crw-r-----   1 root sys	 32, 150 Aug 29 00:02 xkserial@2000:6,cu
       crw-r-----   1 root sys	 32,  23 Aug 29 00:02 xkserial@2000:7
       crw-r-----   1 root sys	 32, 151 Aug 29 00:02 xkserial@2000:7,cu

       /dev/term contain symbolic links to the serial port device nodes in /devices

       # ls -l /dev/term
       /dev/term/0 -> ../../devices/[....]/xkserial@2000:0
       /dev/term/1 -> ../../devices/[....]/xkserial@2000:1
       /dev/term/2 -> ../../devices/[....]/xkserial@2000:2
       /dev/term/3 -> ../../devices/[....]/xkserial@2000:3
       /dev/term/4 -> ../../devices/[....]/xkserial@2000:4
       /dev/term/5 -> ../../devices/[....]/xkserial@2000:5
       /dev/term/6 -> ../../devices/[....]/xkserial@2000:6
       /dev/term/7 -> ../../devices/[....]/xkserial@2000:7

       and /dev/cua contain symbolic links to the dialout port device nodes in /devices

       # ls -l /dev/cua

       /dev/cua/0 -> ../../devices/[....]/xkserial@2000:0,cu
       /dev/cua/1 -> ../../devices/[....]/xkserial@2000:1,cu
       /dev/cua/2 -> ../../devices/[....]/xkserial@2000:2,cu
       /dev/cua/3 -> ../../devices/[....]/xkserial@2000:3,cu
       /dev/cua/4 -> ../../devices/[....]/xkserial@2000:4,cu
       /dev/cua/5 -> ../../devices/[....]/xkserial@2000:5,cu
       /dev/cua/6 -> ../../devices/[....]/xkserial@2000:6,cu
       /dev/cua/7 -> ../../devices/[....]/xkserial@2000:7,cu

FILES

       /dev/term/n     Logical serial port devices

       /dev/cua/n      Logical dialout port devices

       /etc/inittab

       /etc/saf/*

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     | SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       add_drv(1M), devfsadm(1M), drvconfig(1M), pmadm(1M), sacadm(1M), attributes(5), devfs(7FS), attach(9E), ddi_create_minor_node(9F)

       Writing Device Drivers

SunOS 5.10							    8 Nov 2002								 ports(1M)
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