diff --git a/doc/NEWS.Rd b/doc/NEWS.Rd
index 1ebd0b3682..878faf9544 100644
--- a/doc/NEWS.Rd
+++ b/doc/NEWS.Rd
@@ -125,6 +125,11 @@
 
   \subsection{Utilities}{
     \itemize{
+      \item The default HTTP user agent on Linux now includes
+      machine-readable distribution identifiers from \file{os-release} when
+      available.  The \samp{libcurl} download method now uses the same default
+      user agent as the other HTTP methods.
+
       \item \code{tools::texi2pdf()} now reports BibTeX warnings;
       in particular, missing references are now noted by
       \command{R CMD check} when re-building PDF vignettes.
diff --git a/src/library/base/man/options.Rd b/src/library/base/man/options.Rd
index 114bdb27c1..2dba451c56 100644
--- a/src/library/base/man/options.Rd
+++ b/src/library/base/man/options.Rd
@@ -707,12 +707,10 @@ getOption(x, default = NULL)
       HTTP(S) requests by \code{\link{download.file}}, \code{\link{url}}
       and \code{\link{curlGetHeaders}}, or \code{NULL} when requests will
       be made without a user agent header.  The default is
-      \code{"R (\var{version} \var{platform} \var{arch} \var{os})"}
-      except when \samp{libcurl} is used when it is
-      \code{"libcurl/\var{version}"} for the \samp{libcurl} version in use.
-      With \samp{libcurl}, the \code{"R "} prefix is reserved:
-      \code{HTTPUserAgent} with the prefix will be ignored and the default will
-      be used.}
+      \code{"R (\var{version} \var{platform} \var{arch} \var{os})"}.
+      On Linux, machine-readable distribution identifiers from
+      \file{/etc/os-release} or \file{/usr/lib/os-release} are appended when
+      available.}
 
     \item{\code{install.lock}:}{logical: should per-directory package
       locking be used by \code{\link{install.packages}}?  Most useful
diff --git a/src/library/utils/R/readhttp.R b/src/library/utils/R/readhttp.R
index e441ea7882..ffef100132 100644
--- a/src/library/utils/R/readhttp.R
+++ b/src/library/utils/R/readhttp.R
@@ -1,7 +1,7 @@
 #  File src/library/utils/R/readhttp.R
 #  Part of the R package, https://www.R-project.org
 #
-#  Copyright (C) 1995-2012 The R Core Team
+#  Copyright (C) 1995-2026 The R Core Team
 #
 #  This program is free software; you can redistribute it and/or modify
 #  it under the terms of the GNU General Public License as published by
@@ -26,6 +26,35 @@
 }
 
 
+.linuxOSRelease <- function(files = c("/etc/os-release", "/usr/lib/os-release"),
+                            os = R.version$os)
+{
+    if (!startsWith(os, "linux")) return(character())
+
+    files <- files[file_test("-f", files)]
+    if (!length(files)) return(character())
+    lines <- tryCatch(suppressWarnings(readLines(files[1L], warn = FALSE)),
+                      error = function(e) character())
+    if (!length(lines)) return(character())
+
+    value <- function(key) {
+        ## os-release: the last assignment of a key wins
+        line <- rev(grep(paste0("^", key, "="), lines, value = TRUE))[1L]
+        if (is.na(line)) return("")
+        ans <- trimws(substring(line, nchar(key) + 2L))
+        if (grepl('^".*"$', ans) || grepl("^'.*'$", ans))
+            ans <- substring(ans, 2L, nchar(ans) - 1L)
+        if (!grepl("^[A-Za-z0-9._-]+$", ans)) "" else ans
+    }
+
+    ans <- c(distro = value("ID"), version = value("VERSION_ID"),
+             codename = value("VERSION_CODENAME"))
+    ans[nzchar(ans)]
+}
+
 
 defaultUserAgent <- function()
 {
@@ -34,6 +63,11 @@
                       if (length(grep("^darwin", R.version$os))) ## use run-time (vs build)
                         gsub(" ","",tolower(system("uname -sr 2>/dev/null||echo darwin", intern=TRUE)))
                       else R.version$os)
+    distro <- .linuxOSRelease()
+    if (length(distro))
+        Rdetails <- paste0(Rdetails, "; ",
+                           paste(names(distro), distro, sep = "=",
+                                 collapse = "; "))
     paste0("R (", Rdetails, ")")
 }
 
diff --git a/src/library/utils/tests/user-agent.R b/src/library/utils/tests/user-agent.R
new file mode 100644
index 0000000000..4bb2847f8d
--- /dev/null
+++ b/src/library/utils/tests/user-agent.R
@@ -0,0 +1,49 @@
+## Test machine-readable Linux distribution details in the default user agent.
+
+write_os_release <- function(lines) {
+    path <- tempfile()
+    writeLines(lines, path)
+    path
+}
+
+ubuntu <- write_os_release(c(
+    'NAME="Ubuntu"',
+    'ID=ubuntu',
+    'VERSION_ID="26.04"',
+    'VERSION_CODENAME=resolute'
+))
+info <- utils:::.linuxOSRelease(ubuntu, os = "linux-gnu")
+stopifnot(identical(info, c(
+    distro = "ubuntu", version = "26.04", codename = "resolute"
+)))
+
+alpine <- write_os_release(c("ID=alpine", 'VERSION_ID="3.24.1"'))
+info <- utils:::.linuxOSRelease(alpine, os = "linux-musl")
+stopifnot(identical(info, c(distro = "alpine", version = "3.24.1")))
+
+unsafe <- write_os_release(c(
+    "ID=example", "VERSION_ID=1.0", "VERSION_CODENAME=bad/value"
+))
+info <- utils:::.linuxOSRelease(unsafe, os = "linux-gnu")
+stopifnot(identical(info, c(distro = "example", version = "1.0")))
+
+dups <- write_os_release(c("ID=first", "ID=last", 'VERSION_ID="2.0"  '))
+info <- utils:::.linuxOSRelease(dups, os = "linux-gnu")
+stopifnot(identical(info, c(distro = "last", version = "2.0")))
+
+rolling <- write_os_release("ID=arch")
+info <- utils:::.linuxOSRelease(rolling, os = "linux-gnu")
+stopifnot(identical(info, c(distro = "arch")))
+
+stopifnot(!length(utils:::.linuxOSRelease(ubuntu, os = "darwin23")))
+stopifnot(!length(utils:::.linuxOSRelease(tempfile(), os = "linux-gnu")))
+
+dir <- tempfile(); dir.create(dir)
+info <- withCallingHandlers(utils:::.linuxOSRelease(dir, os = "linux-gnu"),
+                            warning = function(w) stop(w))
+stopifnot(!length(info))
+
+unlink(c(ubuntu, alpine, unsafe, dups, rolling, dir), recursive = TRUE)
diff --git a/src/modules/internet/libcurl.c b/src/modules/internet/libcurl.c
index 2b07785d2a..e65e01c6e6 100644
--- a/src/modules/internet/libcurl.c
+++ b/src/modules/internet/libcurl.c
@@ -288,11 +288,8 @@ void curlCommon(CURL *hnd, int redirect, int verify)
     if (TYPEOF(sua) == STRSXP && LENGTH(sua) == 1 ) {
 	const void *vmax = vmaxget();
 	const char *p = translateChar(STRING_ELT(sua, 0));
-	if (p[0] && p[1] && p[2] && p[0] == 'R' && p[1] == ' ' && p[2] == '(') {
-	} else {
-	    Default = 0;
-	    curl_easy_setopt(hnd, CURLOPT_USERAGENT, p);
-	}
+	Default = 0;
+	curl_easy_setopt(hnd, CURLOPT_USERAGENT, p);
 	vmaxset(vmax);
     }
     if (Default) {
diff --git a/tests/download.file.R b/tests/download.file.R
index fa73fceda9..2465fc33be 100644
--- a/tests/download.file.R
+++ b/tests/download.file.R
@@ -61,6 +61,12 @@ with_options <- function(opts, expr) {
 
 tests <- function() {
   cat("- User agent is still set\n")
+  with_options(list(HTTPUserAgent = utils:::defaultUserAgent()), {
+    h <- get_headers()
+    stopifnot(grep_hdr("User-Agent.*R \\(", h))
+  })
+
   with_options(list(HTTPUserAgent = "foobar"), {
     h <- get_headers()
     stopifnot(grep_hdr("User-Agent.*foobar", h))