全部博文（52）
分类： LINUX
2008-11-28 19:29:42
It provides the ability to register additional binary formats to the kernel without compiling an additional module/kernel. Therefore, binfmt_misc needs to know magic numbers at the beginning or the filename extension of the binary.
It works by maintaining a linked list of structs that contain a description of a binary format, including a magic with size (or the filename extension), offset and mask, and the interpreter name. On request it invokes the given interpreter with the original program as argument, as binfmt_java and binfmt_em86 and binfmt_mz do. Since binfmt_misc does not define any default binary-formats, you have to register an additional binary-format.
Each registered handler has an entry in /proc/sys/fs/binfmt_misc.
These files perform the same function as , but their scope is limited to the actual binary format. By cating this file, you also receive all related information about the interpreter/magic of the binfmt.
1 register
To register a new binary format you have to issue the command
echo :name:type:offset:magic:mask:interpreter: > /proc/sys/fs/binfmt_misc/register
with appropriate name (the name for the /proc-dir entry), offset (defaults to 0, if omitted), magic, mask (which can be omitted, defaults to all 0xff) and last but not least, the interpreter that is to be invoked (for example and testing /bin/echo). Type can be M for usual magic matching or E for filename extension matching (give extension in place of magic).
2 status
If you do a cat on this file, you will get the current status (enabled/disabled) of binfmt_misc. Change the status by echoing 0 (disables) or 1 (enables) or -1 (caution: this clears all previously registered binary formats) to status
四 dentry_state
Status of the directory cache. Since directory entries are dynamically allocated and deallocated, this file indicates the current status. It holds six values of which only the first three are used:
Last three values are not used and are always zero.
五 dir-notify-enable
This file controls dnotify, a directory notification mechanism, and will not appear if dnotify support is compiled out. It was introduced with inotify in case some people want to disable dnotify support at runtime.
There are two possible values:
六 file-max
The kernel allocates file handles dynamically, but doesn't free them again at this time.
The value in file-max denotes the maximum number of file handles that the Linux kernel will allocate. When you get a lot of error messages about running out of file handles, you might want to raise this limit. The default value is 10% of RAM in kilobytes
七 file-nr
Historically, the three values in file-nr denoted the number of allocated file handles, the number of allocated but unused file handles, and the maximum number of file handles. Linux 2.6 always reports 0 as the number of free file handles - this is not an error, it just means that the number of allocated file handles exactly matches the number of used file handles.
八 inode-nr
The file inode-nr contains the first two items from .
九 inode-state
inode-state contains two actual numbers and five dummy values. The numbers are:
十 inotify
The following interfaces can be used to limit the amount of kernel memory consumed by the inotify file system event-monitoring mechanism.
1 max_queued_events
The value in this file is used when an application calls inotify_init(2) to set an upper limit on the number of events that can be queued to the corresponding inotify instance. Events in excess of this limit are dropped, but an IN_Q_OVERFLOW event is always generated.
2 max_queued_events
The value in this file is used when an application calls inotify_init(2) to set an upper limit on the number of events that can be queued to the corresponding inotify instance. Events in excess of this limit are dropped, but an IN_Q_OVERFLOW event is always generated.
3 max_user_instances
This specifies an upper limit on the number of inotify instances that can be created per real user ID.
4 max_user_watches
This specifies a limit on the number of watches that can be associated with each inotify instance.
十一 lease-break-time
This file specifies the grace period (in seconds) that the kernel grants to a process holding a file lease after it has sent a signal to that process notifying it that another process is waiting to open the file. If the lease holder does not remove or downgrade the lease within this grace period, the kernel forcibly breaks the lease
十二 leases-enable
This file can be used to enable or disable file leases on a system-wide basis. If this file contains the value 0, leases are disabled. A non-zero value enables leases.
十三 mqueue
This subdirectory contains files that are used for controlling the resources used by POSIX message queues
1 msg_max
msg_max is a read/write file for setting/getting the maximum number of messages in a queue value. In fact it is the limiting value for another (user) limit which is set in mq_open invocation. This attribute of a queue must be less or equal than msg_max.
2 msgsize_max
msgsize_max is a read/write file for setting/getting the maximum message size value (it is every message queue's attribute set during its creation).
3 queues_max
queues_max is a read/write file for setting/getting the maximum number of message queues allowed on the system.
十四 nfs
This subdirectory contains files that allow users to change some NFS parameters
1 nlm_grace_period
Time to wait for client lock daemons to reclaim locks. Allowed values: 0 - 240. The default is 0.
2 nlm_tcpport
Allows explicit setting of TCP port number for lock daemon. The default is 0, meaning no default (choose dynamically).
3 nlm_timeout
Retransmit interval for lock requests. Allowed values: 3 - 20 seconds. The default is 10 seconds.
4 nlm_udpport
Allows explicit setting of UDP port number for lock daemon. The default is 0, meaning no default (choose dynamically).
十五 ntfs-debug
This file exists only if the kernel is compiled with NTFS debugging support (CONFIG_NTFS_DEBUG). Write non-zero value to this file to enable NTFS debug messages. This is disabled by default.
Enabling debug messages results in very significant slowdown of the system, so enable them only if you are experiencing problems with the NTFS file system.
十六 overflowgid
Some filesystems only support 16-bit GIDs, although in Linux GIDs are 32 bits. When one of these filesystems is mounted with writes enabled, any GID that would exceed 65535 is translated to a fixed value before being written to disk.
This sysctl allows you to change the value of the fixed GID. The default is 65534.
十七 overflowuid
Some filesystems only support 16-bit UIDs, although in Linux UIDs are 32 bits. When one of these filesystems is mounted with writes enabled, any UID that would exceed 65535 is translated to a fixed value before being written to disk.
This sysctl allows you to change the value of the fixed UID. The default is 65534
十九 suid_dumpable
The value in this file determines whether core dump files are produced for set-user-ID or otherwise protected/tainted binaries. Three different integer values can be specified:
二十 xfs
This directory contains sysctls corresponding to the XFS filesystem. This directory will not be available if you have no XFS support loaded into the kernel.
1 age_buffer_centisecs
The age at which xfsbufd flushes dirty metadata buffers to disk.
Min: 100
Default: 1500
Max: 720000
2 error_level
A volume knob for error reporting when internal errors occur.This will generate detailed messages & backtraces for filesystem shutdowns, for example. Current threshold values are:
XFS_ERRLEVEL_OFF: 0
XFS_ERRLEVEL_LOW: 1
XFS_ERRLEVEL_HIGH: 5
Min: 0
Default: 3
Max: 11
3 inherit_noatime
Setting this to 1 will cause the "noatime" flag set by the xfs_io (8) chattr command on a directory to be inherited by files in that directory.
Min: 0
Default: 1
Max: 1
4 inherit_nodump
Setting this to 1 will cause the "nodump" flag set by the xfs_io(8) chattr command on a directory to be inherited by files in that directory.
Min: 0
Default: 1
Max: 1
5 inherit_nosymlinks
Setting this to 1 will cause the "nosymlinks" flag set by the xfs_io(8) chattr command on a directory to be inherited by files in that directory.
Min: 0
Default: 0
Max: 1
6 inherit_sync
Setting this to 1 will cause the "sync" flag set by the xfs_io(8) chattr command on a directory to be inherited by files in that directory.
Min: 0
Default: 1
Max: 1
7 irix_sgid_inherit
Controls files created in SGID directories.
If the group ID of the new file does not match the effective group ID or one of the supplementary group IDs of the parent dir, the ISGID bit is cleared if the irix_sgid_inherit compatibility sysctl is set.
Min: 0
Default: 0
Max: 1
8 irix_symlink_mode
Controls whether symlinks are created with mode 0777 (default) or whether their mode is affected by the umask (irix mode).
Min: 0
Default: 0
Max: 1
9 panic_mask
Causes certain error conditions to call BUG(). Value is a bitmask; AND together the tags which represent errors which should cause panics:
This option is intended for debugging only.
Min: 0
Default: 0
Max: 127
10 restrict_chown
Controls whether unprivileged users can use chown to "give away" a file to another user.
Min: 0
Default: 1
Max: 1
11 rotorstep
In "inode32" allocation mode, this option determines how many files the allocator attempts to allocate in the same allocation group before moving to the next allocation group. The intent is to control the rate at which the allocator moves between allocation groups when allocating extents for new files.
Min: 0
Default : 1
Max: 256
12 stats_clear
Setting this to 1 clears accumulated XFS statistics in . It then immediately resets to 0.
Min: 0
Default: 0
Max: 1
13 xfsbufd_centisecs
The interval at which xfsbufd scans the dirty metadata buffers list.
Min: 50
Default: 100
Max: 3000
14 xfssyncd_centisecs
The interval at which the xfssyncd thread flushes metadata out to disk. This thread will flush log activity out, and do some processing on unlinked inodes.
Min: 100
Default: 3000
Max: 720000
