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From 2808e53f785e9ca7fdab286678e784b661b4c185 Mon Sep 17 00:00:00 2001
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From: Zsolt Dollenstein <zsol.zsol@gmail.com>
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Date: Tue, 3 Jul 2018 12:22:29 -0700
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Subject: [PATCH] Add support for opening files for appending
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Addresses part of #8983
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(cherry picked from commit 566b7d23eb747e9c5a74e5647693077b52395fc5)
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Resolves: #1809175
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---
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 man/systemd.exec.xml                          | 16 ++++++----
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 src/core/dbus-execute.c                       | 30 ++++++++++++++-----
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 src/core/execute.c                            | 20 ++++++++++---
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 src/core/execute.h                            |  1 +
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 src/core/load-fragment.c                      | 11 +++++++
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 src/core/main.c                               |  4 +--
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 src/test/test-execute.c                       | 10 +++++++
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 test/meson.build                              |  2 ++
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 .../exec-standardoutput-append.service        | 13 ++++++++
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 .../exec-standardoutput-file.service          | 13 ++++++++
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 10 files changed, 101 insertions(+), 19 deletions(-)
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 create mode 100644 test/test-execute/exec-standardoutput-append.service
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 create mode 100644 test/test-execute/exec-standardoutput-file.service
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diff --git a/man/systemd.exec.xml b/man/systemd.exec.xml
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index bdaed68162..e2a5ede968 100644
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--- a/man/systemd.exec.xml
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+++ b/man/systemd.exec.xml
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@@ -1792,8 +1792,8 @@ SystemCallErrorNumber=EPERM</programlisting>
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         of <option>inherit</option>, <option>null</option>, <option>tty</option>, <option>journal</option>,
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         <option>syslog</option>, <option>kmsg</option>, <option>journal+console</option>,
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         <option>syslog+console</option>, <option>kmsg+console</option>,
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-        <option>file:<replaceable>path</replaceable></option>, <option>socket</option> or
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-        <option>fd:<replaceable>name</replaceable></option>.</para>
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+        <option>file:<replaceable>path</replaceable></option>, <option>append:<replaceable>path</replaceable></option>,
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+        <option>socket</option> or<option>fd:<replaceable>name</replaceable></option>.</para>
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         <para><option>inherit</option> duplicates the file descriptor of standard input for standard output.</para>
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@@ -1824,11 +1824,17 @@ SystemCallErrorNumber=EPERM</programlisting>
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         <para>The <option>file:<replaceable>path</replaceable></option> option may be used to connect a specific file
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         system object to standard output. The semantics are similar to the same option of
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-        <varname>StandardInput=</varname>, see above. If standard input and output are directed to the same file path,
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-        it is opened only once, for reading as well as writing and duplicated. This is particular useful when the
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-        specified path refers to an <constant>AF_UNIX</constant> socket in the file system, as in that case only a
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+        <varname>StandardInput=</varname>, see above. If <replaceable>path</replaceable> refers to a regular file
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+        on the filesystem, it is opened (created if it doesn't exist yet) for writing at the beginning of the file,
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+        but without truncating it.
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+        If standard input and output are directed to the same file path, it is opened only once, for reading as well
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+        as writing and duplicated. This is particularly useful when the specified path refers to an
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+        <constant>AF_UNIX</constant> socket in the file system, as in that case only a
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         single stream connection is created for both input and output.</para>
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+        <para><option>append:<replaceable>path</replaceable></option> is similar to <option>file:<replaceable>path
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+        </replaceable></option> above, but it opens the file in append mode.</para>
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+
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         <para><option>socket</option> connects standard output to a socket acquired via socket activation. The
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         semantics are similar to the same option of <varname>StandardInput=</varname>, see above.</para>
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diff --git a/src/core/dbus-execute.c b/src/core/dbus-execute.c
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index e7c0b893d1..f9527e56b2 100644
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--- a/src/core/dbus-execute.c
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+++ b/src/core/dbus-execute.c
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@@ -1772,7 +1772,10 @@ int bus_exec_context_set_transient_property(
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                 return 1;
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-        } else if (STR_IN_SET(name, "StandardInputFile", "StandardOutputFile", "StandardErrorFile")) {
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+        } else if (STR_IN_SET(name,
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+                              "StandardInputFile",
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+                              "StandardOutputFile", "StandardOutputFileToCreate", "StandardOutputFileToAppend",
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+                              "StandardErrorFile", "StandardErrorFileToCreate", "StandardErrorFileToAppend")) {
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                 const char *s;
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                 r = sd_bus_message_read(message, "s", &s);
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@@ -1796,23 +1799,34 @@ int bus_exec_context_set_transient_property(
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                                 c->std_input = EXEC_INPUT_FILE;
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                                 unit_write_settingf(u, flags|UNIT_ESCAPE_SPECIFIERS, name, "StandardInput=file:%s", s);
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-                        } else if (streq(name, "StandardOutputFile")) {
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+                        } else if (STR_IN_SET(name, "StandardOutputFile", "StandardOutputFileToAppend")) {
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                                 r = free_and_strdup(&c->stdio_file[STDOUT_FILENO], empty_to_null(s));
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                                 if (r < 0)
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                                         return r;
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-                                c->std_output = EXEC_OUTPUT_FILE;
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-                                unit_write_settingf(u, flags|UNIT_ESCAPE_SPECIFIERS, name, "StandardOutput=file:%s", s);
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-
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+                                if (streq(name, "StandardOutputFile")) {
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+                                        c->std_output = EXEC_OUTPUT_FILE;
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+                                        unit_write_settingf(u, flags|UNIT_ESCAPE_SPECIFIERS, name, "StandardOutput=file:%s", s);
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+                                } else {
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+                                        assert(streq(name, "StandardOutputFileToAppend"));
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+                                        c->std_output = EXEC_OUTPUT_FILE_APPEND;
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+                                        unit_write_settingf(u, flags|UNIT_ESCAPE_SPECIFIERS, name, "StandardOutput=append:%s", s);
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+                                }
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                         } else {
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-                                assert(streq(name, "StandardErrorFile"));
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+                                assert(STR_IN_SET(name, "StandardErrorFile", "StandardErrorFileToAppend"));
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                                 r = free_and_strdup(&c->stdio_file[STDERR_FILENO], empty_to_null(s));
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                                 if (r < 0)
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                                         return r;
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-                                c->std_error = EXEC_OUTPUT_FILE;
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-                                unit_write_settingf(u, flags|UNIT_ESCAPE_SPECIFIERS, name, "StandardError=file:%s", s);
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+                                if (streq(name, "StandardErrorFile")) {
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+                                        c->std_error = EXEC_OUTPUT_FILE;
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+                                        unit_write_settingf(u, flags|UNIT_ESCAPE_SPECIFIERS, name, "StandardOutput=file:%s", s);
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+                                } else {
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+                                      assert(streq(name, "StandardErrorFileToAppend"));
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+                                      c->std_error = EXEC_OUTPUT_FILE_APPEND;
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+                                      unit_write_settingf(u, flags|UNIT_ESCAPE_SPECIFIERS, name, "StandardOutput=append:%s", s);
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+                                }
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                         }
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                 }
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diff --git a/src/core/execute.c b/src/core/execute.c
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index f012023224..3c54ac1110 100644
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--- a/src/core/execute.c
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+++ b/src/core/execute.c
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@@ -89,6 +89,7 @@
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 #include "strv.h"
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 #include "syslog-util.h"
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 #include "terminal-util.h"
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+#include "umask-util.h"
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 #include "unit.h"
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 #include "user-util.h"
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 #include "util.h"
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@@ -675,9 +676,10 @@ static int setup_output(
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                 (void) fd_nonblock(named_iofds[fileno], false);
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                 return dup2(named_iofds[fileno], fileno) < 0 ? -errno : fileno;
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-        case EXEC_OUTPUT_FILE: {
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+        case EXEC_OUTPUT_FILE:
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+        case EXEC_OUTPUT_FILE_APPEND: {
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                 bool rw;
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-                int fd;
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+                int fd, flags;
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                 assert(context->stdio_file[fileno]);
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@@ -687,11 +689,16 @@ static int setup_output(
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                 if (rw)
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                         return dup2(STDIN_FILENO, fileno) < 0 ? -errno : fileno;
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-                fd = acquire_path(context->stdio_file[fileno], O_WRONLY, 0666 & ~context->umask);
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+                flags = O_WRONLY;
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+                if (o == EXEC_OUTPUT_FILE_APPEND)
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+                        flags |= O_APPEND;
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+
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+                fd = acquire_path(context->stdio_file[fileno], flags, 0666 & ~context->umask);
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+
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                 if (fd < 0)
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                         return fd;
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-                return move_fd(fd, fileno, false);
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+                return move_fd(fd, fileno, 0);
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         }
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         default:
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@@ -4168,8 +4175,12 @@ void exec_context_dump(const ExecContext *c, FILE* f, const char *prefix) {
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                 fprintf(f, "%sStandardInputFile: %s\n", prefix, c->stdio_file[STDIN_FILENO]);
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         if (c->std_output == EXEC_OUTPUT_FILE)
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                 fprintf(f, "%sStandardOutputFile: %s\n", prefix, c->stdio_file[STDOUT_FILENO]);
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+        if (c->std_output == EXEC_OUTPUT_FILE_APPEND)
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+                fprintf(f, "%sStandardOutputFileToAppend: %s\n", prefix, c->stdio_file[STDOUT_FILENO]);
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         if (c->std_error == EXEC_OUTPUT_FILE)
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                 fprintf(f, "%sStandardErrorFile: %s\n", prefix, c->stdio_file[STDERR_FILENO]);
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+        if (c->std_error == EXEC_OUTPUT_FILE_APPEND)
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+                fprintf(f, "%sStandardErrorFileToAppend: %s\n", prefix, c->stdio_file[STDERR_FILENO]);
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         if (c->tty_path)
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                 fprintf(f,
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@@ -5111,6 +5122,7 @@ static const char* const exec_output_table[_EXEC_OUTPUT_MAX] = {
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         [EXEC_OUTPUT_SOCKET] = "socket",
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         [EXEC_OUTPUT_NAMED_FD] = "fd",
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         [EXEC_OUTPUT_FILE] = "file",
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+        [EXEC_OUTPUT_FILE_APPEND] = "append",
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 };
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 DEFINE_STRING_TABLE_LOOKUP(exec_output, ExecOutput);
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diff --git a/src/core/execute.h b/src/core/execute.h
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index 2266355962..86c1cee84c 100644
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--- a/src/core/execute.h
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+++ b/src/core/execute.h
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@@ -57,6 +57,7 @@ typedef enum ExecOutput {
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         EXEC_OUTPUT_SOCKET,
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         EXEC_OUTPUT_NAMED_FD,
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         EXEC_OUTPUT_FILE,
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+        EXEC_OUTPUT_FILE_APPEND,
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         _EXEC_OUTPUT_MAX,
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         _EXEC_OUTPUT_INVALID = -1
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 } ExecOutput;
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diff --git a/src/core/load-fragment.c b/src/core/load-fragment.c
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index 2082166afb..9b2724307d 100644
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--- a/src/core/load-fragment.c
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+++ b/src/core/load-fragment.c
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@@ -1016,6 +1016,17 @@ int config_parse_exec_output(
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                 eo = EXEC_OUTPUT_FILE;
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+        } else if ((n = startswith(rvalue, "append:"))) {
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+
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+                r = unit_full_printf(u, n, &resolved);
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+                if (r < 0)
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+                        return log_syntax(unit, LOG_ERR, filename, line, r, "Failed to resolve unit specifiers in %s: %m", n);
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+
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+                r = path_simplify_and_warn(resolved, PATH_CHECK_ABSOLUTE | PATH_CHECK_FATAL, unit, filename, line, lvalue);
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+                if (r < 0)
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+                        return -ENOEXEC;
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+
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+                eo = EXEC_OUTPUT_FILE_APPEND;
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         } else {
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                 eo = exec_output_from_string(rvalue);
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                 if (eo < 0) {
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diff --git a/src/core/main.c b/src/core/main.c
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index 9f238a8430..25536054b3 100644
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--- a/src/core/main.c
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+++ b/src/core/main.c
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@@ -620,8 +620,8 @@ static int config_parse_output_restricted(
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                 return 0;
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         }
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-        if (IN_SET(t, EXEC_OUTPUT_SOCKET, EXEC_OUTPUT_NAMED_FD, EXEC_OUTPUT_FILE)) {
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-                log_syntax(unit, LOG_ERR, filename, line, 0, "Standard output types socket, fd:, file: are not supported as defaults, ignoring: %s", rvalue);
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+        if (IN_SET(t, EXEC_OUTPUT_SOCKET, EXEC_OUTPUT_NAMED_FD, EXEC_OUTPUT_FILE, EXEC_OUTPUT_FILE_APPEND)) {
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+                log_syntax(unit, LOG_ERR, filename, line, 0, "Standard output types socket, fd:, file:, append: are not supported as defaults, ignoring: %s", rvalue);
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                 return 0;
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         }
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diff --git a/src/test/test-execute.c b/src/test/test-execute.c
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index 637ffe96bb..0f8dc883b1 100644
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--- a/src/test/test-execute.c
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+++ b/src/test/test-execute.c
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@@ -651,6 +651,14 @@ static void test_exec_standardinput(Manager *m) {
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         test(m, "exec-standardinput-file.service", 0, CLD_EXITED);
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 }
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+static void test_exec_standardoutput(Manager *m) {
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+        test(m, "exec-standardoutput-file.service", 0, CLD_EXITED);
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+}
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+
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+static void test_exec_standardoutput_append(Manager *m) {
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+        test(m, "exec-standardoutput-append.service", 0, CLD_EXITED);
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+}
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+
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 static int run_tests(UnitFileScope scope, const test_function_t *tests) {
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         const test_function_t *test = NULL;
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         _cleanup_(manager_freep) Manager *m = NULL;
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@@ -698,6 +706,8 @@ int main(int argc, char *argv[]) {
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                 test_exec_restrictnamespaces,
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                 test_exec_runtimedirectory,
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                 test_exec_standardinput,
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+                test_exec_standardoutput,
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+                test_exec_standardoutput_append,
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                 test_exec_supplementarygroups,
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                 test_exec_systemcallerrornumber,
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                 test_exec_systemcallfilter,
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diff --git a/test/meson.build b/test/meson.build
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index fb9f2cdb9b..4d1c51048c 100644
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--- a/test/meson.build
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+++ b/test/meson.build
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@@ -115,6 +115,8 @@ test_data_files = '''
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         test-execute/exec-specifier@.service
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         test-execute/exec-standardinput-data.service
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         test-execute/exec-standardinput-file.service
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+        test-execute/exec-standardoutput-file.service
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+        test-execute/exec-standardoutput-append.service
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         test-execute/exec-supplementarygroups-multiple-groups-default-group-user.service
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         test-execute/exec-supplementarygroups-multiple-groups-withgid.service
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         test-execute/exec-supplementarygroups-multiple-groups-withuid.service
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diff --git a/test/test-execute/exec-standardoutput-append.service b/test/test-execute/exec-standardoutput-append.service
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new file mode 100644
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index 0000000000..8983bb056b
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--- /dev/null
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+++ b/test/test-execute/exec-standardoutput-append.service
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@@ -0,0 +1,13 @@
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+[Unit]
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+Description=Test for StandardOutput=append:
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+
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+[Service]
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+ExecStartPre=sh -c 'printf "hello\n" > /tmp/test-exec-standardoutput-output'
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+ExecStartPre=sh -c 'printf "hello\nhello\n" > /tmp/test-exec-standardoutput-expected'
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+StandardInput=data
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+StandardInputText=hello
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+StandardOutput=append:/tmp/test-exec-standardoutput-output
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+StandardError=null
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+ExecStart=cat
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+ExecStart=cmp /tmp/test-exec-standardoutput-output /tmp/test-exec-standardoutput-expected
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+Type=oneshot
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diff --git a/test/test-execute/exec-standardoutput-file.service b/test/test-execute/exec-standardoutput-file.service
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new file mode 100644
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index 0000000000..71e2604b94
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--- /dev/null
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+++ b/test/test-execute/exec-standardoutput-file.service
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@@ -0,0 +1,13 @@
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+[Unit]
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+Description=Test for StandardOutput=file:
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+
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+[Service]
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+ExecStartPre=sh -c 'printf "nooo\nhello\n" > /tmp/test-exec-standardoutput-output'
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+ExecStartPre=sh -c 'printf "hello\nello\n" > /tmp/test-exec-standardoutput-expected'
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+StandardInput=data
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+StandardInputText=hello
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+StandardOutput=file:/tmp/test-exec-standardoutput-output
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+StandardError=null
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+ExecStart=cat
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+ExecStart=cmp /tmp/test-exec-standardoutput-expected /tmp/test-exec-standardoutput-output
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+Type=oneshot