diff --git a/applications/test/fileName/Test-fileName.C b/applications/test/fileName/Test-fileName.C
index 8a1568e4a4..4d44bc358e 100644
--- a/applications/test/fileName/Test-fileName.C
+++ b/applications/test/fileName/Test-fileName.C
@@ -633,10 +633,10 @@ int main(int argc, char *argv[])
 
         fileName::Type lnAType = lnA.type(false);
 
-        if (lnAType != fileName::LINK)
+        if (lnAType != fileName::SYMLINK)
         {
             FatalErrorIn("Test-fileName") << "Type of softlink " << lnA
-                << " should be " << fileName::LINK
+                << " should be " << fileName::SYMLINK
                 << " but is " << lnAType << exit(FatalError);
         }
 
@@ -655,10 +655,10 @@ int main(int argc, char *argv[])
                 << endl;
 
             Foam::cp(lnA, lnB, false);
-            if (lnB.type(false) != fileName::LINK)
+            if (lnB.type(false) != fileName::SYMLINK)
             {
                 FatalErrorIn("Test-fileName") << "Type of softlink " << lnB
-                    << " should be " << fileName::LINK
+                    << " should be " << fileName::SYMLINK
                     << " but is " << lnB.type(false) << exit(FatalError);
             }
             if (lnB.type(true) != fileName::DIRECTORY)
diff --git a/applications/utilities/parallelProcessing/redistributePar/loadOrCreateMesh.C b/applications/utilities/parallelProcessing/redistributePar/loadOrCreateMesh.C
index efa593f075..23969883b3 100644
--- a/applications/utilities/parallelProcessing/redistributePar/loadOrCreateMesh.C
+++ b/applications/utilities/parallelProcessing/redistributePar/loadOrCreateMesh.C
@@ -459,7 +459,7 @@ bool Foam::removeEmptyDir(const fileName& path)
             Foam::readDir
             (
                 path,
-                fileName::LINK,
+                fileName::SYMLINK,
                 false,                  // filterGz
                 false                   // followLink
             )
diff --git a/src/OSspecific/MSwindows/MSwindows.C b/src/OSspecific/MSwindows/MSwindows.C
index 2443044120..37ef5d356e 100644
--- a/src/OSspecific/MSwindows/MSwindows.C
+++ b/src/OSspecific/MSwindows/MSwindows.C
@@ -7,7 +7,7 @@
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
     Copyright (C) 2011 Symscape
-    Copyright (C) 2016-2021 OpenCFD Ltd.
+    Copyright (C) 2016-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -83,7 +83,7 @@ namespace Foam
 
 
     // Move file, overwriting existing
-    static bool renameFile(const fileName& src, const fileName& dst)
+    static bool renameFile(const std::string& src, const std::string& dst)
     {
         constexpr const int flags
         (
@@ -132,7 +132,7 @@ class directoryIterator
 public:
 
     //- Construct for dirName, optionally allowing hidden files/dirs
-    directoryIterator(const fileName& dirName, bool allowHidden = false)
+    directoryIterator(const std::string& dirName, bool allowHidden = false)
     :
         handle_(INVALID_HANDLE_VALUE),
         exists_(false),
@@ -170,13 +170,13 @@ public:
     // Member Functions
 
         //- Directory existed for opening
-        bool exists() const
+        bool exists() const noexcept
         {
             return exists_;
         }
 
         //- Directory pointer is valid
-        bool good() const
+        bool good() const noexcept
         {
             return (INVALID_HANDLE_VALUE != handle_);
         }
@@ -192,7 +192,7 @@ public:
         }
 
         //- The current item
-        const std::string& val() const
+        const std::string& val() const noexcept
         {
             return item_;
         }
@@ -225,13 +225,13 @@ public:
     // Member Operators
 
         //- Same as good()
-        operator bool() const
+        operator bool() const noexcept
         {
             return good();
         }
 
         //- Same as val()
-        const std::string& operator*() const
+        const std::string& operator*() const noexcept
         {
             return val();
         }
@@ -407,7 +407,7 @@ bool Foam::setEnv
 }
 
 
-Foam::string Foam::hostName(bool)
+Foam::string Foam::hostName()
 {
     const DWORD bufLen = MAX_COMPUTERNAME_LENGTH + 1;
     TCHAR buf[bufLen];
@@ -417,12 +417,20 @@ Foam::string Foam::hostName(bool)
 }
 
 
+// DEPRECATED (2022-01)
+Foam::string Foam::hostName(bool)
+{
+    return Foam::hostName();
+}
+
+
+// DEPRECATED (2022-01)
 Foam::string Foam::domainName()
 {
     // Could use ::gethostname and ::gethostbyname like POSIX.C, but would
     // then need to link against ws_32. Prefer to minimize dependencies.
 
-    return string::null;
+    return string();
 }
 
 
@@ -452,7 +460,7 @@ Foam::fileName Foam::home()
 
     if (env.empty())
     {
-        env  = Foam::getEnv("USERPROFILE");
+        env = Foam::getEnv("USERPROFILE");
     }
 
     return env;
@@ -595,21 +603,21 @@ Foam::fileName::Type Foam::type
     // Ignore an empty name => always UNDEFINED
     if (name.empty())
     {
-        return fileName::UNDEFINED;
+        return fileName::Type::UNDEFINED;
     }
 
     const DWORD m = ::GetFileAttributes(name.c_str());
 
     if (ms_isreg(m))
     {
-        return fileName::FILE;
+        return fileName::Type::FILE;
     }
     else if (ms_isdir(m))
     {
-        return fileName::DIRECTORY;
+        return fileName::Type::DIRECTORY;
     }
 
-    return fileName::UNDEFINED;
+    return fileName::Type::UNDEFINED;
 }
 
 
diff --git a/src/OSspecific/MSwindows/MSwindows.H b/src/OSspecific/MSwindows/MSwindows.H
index 00ce5b2a7d..3d8cb8a127 100644
--- a/src/OSspecific/MSwindows/MSwindows.H
+++ b/src/OSspecific/MSwindows/MSwindows.H
@@ -35,8 +35,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef MSwindows_H
-#define MSwindows_H
+#ifndef Foam_MSwindows_H
+#define Foam_MSwindows_H
 
 #include "className.H"
 
diff --git a/src/OSspecific/POSIX/POSIX.C b/src/OSspecific/POSIX/POSIX.C
index 5e5d8c12d1..c4935ff499 100644
--- a/src/OSspecific/POSIX/POSIX.C
+++ b/src/OSspecific/POSIX/POSIX.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2016-2021 OpenCFD Ltd.
+    Copyright (C) 2016-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -142,7 +142,7 @@ public:
     // Constructors
 
         //- Construct for dirName, optionally allowing hidden files/dirs
-        directoryIterator(const fileName& dirName, bool allowHidden = false)
+        directoryIterator(const std::string& dirName, bool allowHidden = false)
         :
             dirptr_(nullptr),
             exists_(false),
@@ -168,13 +168,13 @@ public:
     // Member Functions
 
         //- Directory open succeeded
-        bool exists() const
+        bool exists() const noexcept
         {
             return exists_;
         }
 
         //- Directory pointer is valid
-        bool good() const
+        bool good() const noexcept
         {
             return dirptr_;
         }
@@ -190,7 +190,7 @@ public:
         }
 
         //- The current item
-        const std::string& val() const
+        const std::string& val() const noexcept
         {
             return item_;
         }
@@ -220,13 +220,13 @@ public:
     // Member Operators
 
         //- Same as good()
-        operator bool() const
+        operator bool() const noexcept
         {
             return good();
         }
 
         //- Same as val()
-        const std::string& operator*() const
+        const std::string& operator*() const noexcept
         {
             return val();
         }
@@ -302,25 +302,36 @@ bool Foam::setEnv
 }
 
 
-Foam::string Foam::hostName(bool full)
+Foam::string Foam::hostName()
 {
     char buf[128];
     ::gethostname(buf, sizeof(buf));
+    return buf;
+}
 
+
+// DEPRECATED (2022-01)
+Foam::string Foam::hostName(bool full)
+{
     // implementation as per hostname from net-tools
     if (full)
     {
+        char buf[128];
+        ::gethostname(buf, sizeof(buf));
+
         struct hostent *hp = ::gethostbyname(buf);
         if (hp)
         {
             return hp->h_name;
         }
+        return buf;
     }
 
-    return buf;
+    return Foam::hostName();
 }
 
 
+// DEPRECATED (2022-01)
 Foam::string Foam::domainName()
 {
     char buf[128];
@@ -338,7 +349,7 @@ Foam::string Foam::domainName()
         }
     }
 
-    return string::null;
+    return string();
 }
 
 
@@ -713,12 +724,16 @@ mode_t Foam::mode(const fileName& name, const bool followLink)
 }
 
 
-Foam::fileName::Type Foam::type(const fileName& name, const bool followLink)
+Foam::fileName::Type Foam::type
+(
+    const fileName& name,
+    const bool followLink
+)
 {
     // Ignore an empty name => always UNDEFINED
     if (name.empty())
     {
-        return fileName::UNDEFINED;
+        return fileName::Type::UNDEFINED;
     }
 
     if (POSIX::debug)
@@ -730,18 +745,18 @@ Foam::fileName::Type Foam::type(const fileName& name, const bool followLink)
 
     if (S_ISREG(m))
     {
-        return fileName::FILE;
+        return fileName::Type::FILE;
     }
     else if (S_ISLNK(m))
     {
-        return fileName::LINK;
+        return fileName::Type::SYMLINK;
     }
     else if (S_ISDIR(m))
     {
-        return fileName::DIRECTORY;
+        return fileName::Type::DIRECTORY;
     }
 
-    return fileName::UNDEFINED;
+    return fileName::Type::UNDEFINED;
 }
 
 
@@ -1033,7 +1048,7 @@ bool Foam::cp(const fileName& src, const fileName& dest, const bool followLink)
             return false;
         }
     }
-    else if (srcType == fileName::LINK)
+    else if (srcType == fileName::SYMLINK)
     {
         // If dest is a directory, create the destination file name.
         if (destFile.type() == fileName::DIRECTORY)
diff --git a/src/OSspecific/POSIX/POSIX.H b/src/OSspecific/POSIX/POSIX.H
index 10c04e8b39..f31801ebbf 100644
--- a/src/OSspecific/POSIX/POSIX.H
+++ b/src/OSspecific/POSIX/POSIX.H
@@ -34,8 +34,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef POSIX_H
-#define POSIX_H
+#ifndef Foam_POSIX_H
+#define Foam_POSIX_H
 
 #include "className.H"
 
diff --git a/src/OpenFOAM/db/IOstreams/Fstreams/fstreamPointers.C b/src/OpenFOAM/db/IOstreams/Fstreams/fstreamPointers.C
index 60aecb5d89..612f97ca3a 100644
--- a/src/OpenFOAM/db/IOstreams/Fstreams/fstreamPointers.C
+++ b/src/OpenFOAM/db/IOstreams/Fstreams/fstreamPointers.C
@@ -52,7 +52,7 @@ namespace Foam
 
         const fileName::Type pathType = Foam::type(otherName, false);
 
-        if (pathType == fileName::FILE || pathType == fileName::LINK)
+        if (pathType == fileName::FILE || pathType == fileName::SYMLINK)
         {
             Foam::rm(otherName);
         }
@@ -60,7 +60,7 @@ namespace Foam
         // Disallow writing into symlinked files.
         // Eg, avoid problems with symlinked initial fields
 
-        if (!append && Foam::type(targetName, false) == fileName::LINK)
+        if (!append && Foam::type(targetName, false) == fileName::SYMLINK)
         {
             Foam::rm(targetName);
         }
diff --git a/src/OpenFOAM/global/etcFiles/etcFiles.C b/src/OpenFOAM/global/etcFiles/etcFiles.C
index 680bcee603..d7f68398a2 100644
--- a/src/OpenFOAM/global/etcFiles/etcFiles.C
+++ b/src/OpenFOAM/global/etcFiles/etcFiles.C
@@ -218,7 +218,7 @@ static inline bool accept
 )
 {
     // followLink(true), checkGzip(true)
-    // -> returns (UNDEFINED | FILE | DIRECTORY), no need to check for (LINK)
+    // -> returns (UNDEFINED | FILE | DIRECTORY), no need to check for (SYMLINK)
     const auto t = name.type(true, true);
 
     return
diff --git a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
index 2cc6ad7f00..6c0e2c4db5 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperation.H
@@ -38,8 +38,8 @@ Description
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef fileOperation_H
-#define fileOperation_H
+#ifndef Foam_fileOperation_H
+#define Foam_fileOperation_H
 
 #include "ISstream.H"
 #include "Ostream.H"
@@ -262,7 +262,7 @@ public:
                 const bool followLink = true
             ) const = 0;
 
-            //- Return the file type: DIRECTORY, FILE or LINK
+            //- Return the file type: DIRECTORY, FILE or SYMLINK
             virtual fileName::Type type
             (
                 const fileName&,
diff --git a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H
index f2b5b3df58..2b5c959df1 100644
--- a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H
@@ -59,8 +59,8 @@ Description
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef fileOperations_masterUncollatedFileOperation_H
-#define fileOperations_masterUncollatedFileOperation_H
+#ifndef Foam_fileOperations_masterUncollatedFileOperation_H
+#define Foam_fileOperations_masterUncollatedFileOperation_H
 
 #include "fileOperation.H"
 #include "OSspecific.H"
@@ -515,7 +515,7 @@ public:
                 const bool followLink = true
             ) const;
 
-            //- Return the file type: DIRECTORY, FILE or LINK
+            //- Return the file type: DIRECTORY, FILE or SYMLINK
             virtual fileName::Type type
             (
                 const fileName&,
diff --git a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.H b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.H
index fc5d7b1b8d..310bf07efb 100644
--- a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.H
@@ -32,8 +32,8 @@ Description
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef fileOperations_uncollatedFileOperation_H
-#define fileOperations_uncollatedFileOperation_H
+#ifndef Foam_fileOperations_uncollatedFileOperation_H
+#define Foam_fileOperations_uncollatedFileOperation_H
 
 #include "fileOperation.H"
 #include "OSspecific.H"
@@ -110,7 +110,7 @@ public:
                 const bool followLink = true
             ) const;
 
-            //- Return the file type: DIRECTORY, FILE or LINK
+            //- Return the file type: DIRECTORY, FILE or SYMLINK
             virtual fileName::Type type
             (
                 const fileName&,
diff --git a/src/OpenFOAM/include/OSspecific.H b/src/OpenFOAM/include/OSspecific.H
index df9907034b..0a5992b64a 100644
--- a/src/OpenFOAM/include/OSspecific.H
+++ b/src/OpenFOAM/include/OSspecific.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2016-2018 OpenCFD Ltd.
+    Copyright (C) 2016-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -36,8 +36,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef OSspecific_H
-#define OSspecific_H
+#ifndef Foam_OSspecific_H
+#define Foam_OSspecific_H
 
 #include "fileNameList.H"
 #include "stringList.H"
@@ -82,10 +82,16 @@ FOAM_DEPRECATED_FOR(2020-05, "hasEnv() function")
 inline bool env(const std::string& envName) { return Foam::hasEnv(envName); }
 
 //- Return the system's host name, as per hostname(1)
-//  \note the full name (as per the '-f' option) may be unreliable
-string hostName(bool full=false);
+string hostName();
 
-//- Return the system's domain name, as per hostname(1) with the '-d' option
+//- Deprecated(2022-01) full hostname resolution may be unreliable
+//  \deprecated(2022-01) - use hostname() function without parameter
+FOAM_DEPRECATED_FOR(2022-01, "hostname() function without parameter")
+string hostName(bool full);
+
+//- Deprecated(2022-01) domain name resolution may be unreliable
+//  \deprecated(2022-01) - avoid usage entirely
+FOAM_DEPRECATED_FOR(2022-01, "nothing : avoid using at all")
 string domainName();
 
 //- Return the user's login name
diff --git a/src/OpenFOAM/primitives/strings/fileName/fileName.H b/src/OpenFOAM/primitives/strings/fileName/fileName.H
index 41ef3f9c03..32e4cc5f7a 100644
--- a/src/OpenFOAM/primitives/strings/fileName/fileName.H
+++ b/src/OpenFOAM/primitives/strings/fileName/fileName.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2016-2021 OpenCFD Ltd.
+    Copyright (C) 2016-2022 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -45,8 +45,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef fileName_H
-#define fileName_H
+#ifndef Foam_fileName_H
+#define Foam_fileName_H
 
 #include "word.H"
 
@@ -81,9 +81,10 @@ public:
     enum Type
     {
         UNDEFINED = 0,  //!< Undefined type
-        FILE = 1,       //!< A file
+        FILE = 1,       //!< A regular file
         DIRECTORY = 2,  //!< A directory
-        LINK = 4        //!< A symlink
+        SYMLINK = 4,    //!< A symbolic link
+        LINK = SYMLINK  //!< Same as symlink
     };
 
 
@@ -225,9 +226,9 @@ public:
     // Interrogation
 
         //- Return the directory entry type:
-        //- UNDEFINED, FILE, DIRECTORY (or LINK).
+        //- UNDEFINED, FILE, DIRECTORY (or SYMLINK).
         //
-        //  \param followLink when false it will return LINK for a symlink
+        //  \param followLink when false it will return SYMLINK for a symlink
         //     rather than following it.
         //  \param checkGzip add an additional test for a gzip FILE
         Type type(bool followLink=true, bool checkGzip=false) const;