FD column in linux command lsof means a lot ....

lsof gives a ton of information about the files and devices that are open on a system. FD has always wondered me with some wierd numbers/characters. Atlast I bothered to look at it for knowing whether tcpdump has started or not to sniff the device and realized it gives details about the what kind of device/file is opened and the permissions etc.


From the man page,

       FD         is the File Descriptor number of the file or:

                       cwd  current working directory;
                       Lnn  library references (AIX);
                       err  FD information error (see NAME column);
                       jld  jail directory (FreeBSD);
                       ltx  shared library text (code and data);
                       Mxx  hex memory-mapped type number xx.
                       m86  DOS Merge mapped file;
                       mem  memory-mapped file;
                       mmap memory-mapped device;
                       pd   parent directory;
                       rtd  root directory;
                       tr   kernel trace file (OpenBSD);
                       txt  program text (code and data);
                       v86  VP/ix mapped file;

                  FD is followed by one of these characters, describing the mode under which the file is open:

                       r for read access;
                       w for write access;
                       u for read and write access;
                       space if mode unknown and no lock
                            character follows;
                       `-' if mode unknown and lock
                            character follows.

                  The mode character is followed by one of these lock characters, describing the type of lock applied to the file:

                       N for a Solaris NFS lock of unknown type;
                       r for read lock on part of the file;
                       R for a read lock on the entire file;
                       w for a write lock on part of the file;
                       W for a write lock on the entire file;
                       u for a read and write lock of any length;
                       U for a lock of unknown type;
                       x for an SCO OpenServer Xenix lock on part      of the file;
                       X for an SCO OpenServer Xenix lock on the      entire file;
                       space if there is no lock

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