In computer science, a flag is a value that acts as a signal for a function or process. The value of the flag is used to determine the next step of a program. Flags are often binary flags, which contain a boolean value (true or false). However, not all flags are binary, meaning they can store a range of values.

a flag is a value

Flags are often binary flags, which contain a boolean value (true or false).

The open file table contains several pieces of information about each file:

the current offset (the next position to be accessed in the file)
a reference count (we'll explain below in the section about fork())
the file mode (permissions),
the flags passed into the open() (read-only, write-only, create, &c),
a pointer to an in-RAM version of the inode (a slightly light-weight version of the inode for each open file is kept in RAM -- others are on disk), and a structure that contains pointers to all of the .
A pointer to the structure containing pointers to the functions that implement the behaviors like read(), write(), close(), lseek(), &c on the file system that contains this file. This is the same structure we looked at last week when we discussed the file system interface to I/O devices.

DistinguishedName : CN=user1,OU=Users,OU=Lab,DC=example,DC=com

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DistinguishedName : CN=Users,CN=Builtin,DC=example,DC=com

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<Realm
   className="org.apache.catalina.realm.JNDIRealm"
   debug="99"
   connectionURL="ldap://example.com:389"
   authentication="simple"
   referrals="follow"
   connectionName="cn=administrator,cn=users,dc=example,dc=com"
   connectionPassword="##########"
   userSearch="(sAMAccountName={0})"
   userBase="cn=users,dc=example,dc=com"
   userSubtree="true"
   userRoleName="memberOf"
   roleSearch="(member={0})"
   roleName="cn"
   roleSubtree="true"
   roleBase="cn=users,cn=builtin,dc=example,dc=com"/>

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You can start with the POSIX spec. From there, read about the "controlling terminal" of a process.

But just for example... /dev/tty is how a command like "ssh" can read your password even if its standard input comes from somewhere else:

tar cf - . | ssh dest 'tar xf -'

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If ssh decides to prompt you for a password, it will read it from /dev/tty instead of stdin.

Conceptually, /dev/tty is "the keyboard and text terminal". More or less.

/dev/tty is how a command like "ssh" can read your password even if its standard input comes from somewhere else

man find > test.txt

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less test.txt

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lsof | grep 'less'

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COMMAND  PID    USER  FD   TYPE  DEVICE  SIZE/OFF  NODE       NAME
less     24565  root  cwd  DIR   0,38    4096      21473055   /
less     24565  root  rtd  DIR   0,38    4096      21473055   /
less     24565  root  txt  REG   0,38    149944    22143102   /usr/bin/less
less     24565  root  mem  REG   9,1               22143102   /usr/bin/less (path dev=0,38)
less     24565  root  mem  REG   9,1               22135172   /usr/lib/locale/locale-archive-rpm (path dev=0,38)
less     24565  root  mem  REG   9,1               21741879   /lib64/libc-2.12.so (path dev=0,38)
less     24565  root  mem  REG   9,1               22265955   /usr/local/lib/libpcre.so.0.0.1 (path dev=0,38)
less     24565  root  mem  REG   9,1               21741743   /lib64/libtinfo.so.5.7 (path dev=0,38)
less     24565  root  mem  REG   9,1               21741946   /lib64/ld-2.12.so (path dev=0,38)
less     24565  root  0u   CHR   136,1   0t0       4          /dev/pts/1
less     24565  root  1u   CHR   136,1   0t0       4          /dev/pts/1
less     

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Dentries live in RAM and are never saved to disc:

.           inode-number-current-directory
..          inode-number-parent-directory
filename_1  inode-number-A   
filename_2  inode-number-B
et cetera...

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.           inode-number-current-directory
..          inode-number-parent-directory

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Blocks: 8

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filename_1  inode-number-A

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Dentries live in RAM and are never saved to disc:

struct fdtable {
        [...]
};

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/*
 * Open file table structure
 */
struct files_struct {
        [...]
};

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Per Process File Information

struct files_struct { /* kept within task_struct (PCB) */
        [...]
};

The count variable tracks the number of files the process has open