问题
I got several uids like this: 10022, 10011, 1000
Actually I know the usernames of them are u0_a22, u0_a11, system.
But the question is how can I get the username using codes? There is no /etc/passwd file at all..
回答1:
I wrote a utility class to get the UID/GID name by hardcoding values from android_filesystem_config.h.
Usage:
String uid = AndroidFilesystemConfig.getNameForId(1000);
AndroidFilesystemConfig.java
import android.os.Build;
import android.util.SparseArray;
import java.util.Locale;
/**
* <p>System Users and Groups for the Android platform as specified in
* <a href="https://android.googlesource.com/platform/system/core/+/master/include/private/android_filesystem_config.h">android_filesystem_config.h</a>.</p>
*
* <p>Last updated: April 20th, 2016</p>
*
* <p><b>Note:</b> Some OEMs may have specific UIDs for other system users not in this class.</p>
*/
public class AndroidFilesystemConfig {
/* first app user */
private static final int AID_APP = 10000;
/* offset for uid ranges for each user */
private static final int AID_USER = 100000;
/* start of gids for apps in each user to share */
private static final int AID_SHARED_GID_START = 50000;
/* end of gids for apps in each user to share */
private static final int AID_SHARED_GID_END = 59999;
private static final SparseArray<String> SYSTEM_IDS = new SparseArray<>();
static {
putSystemId(0, "root"); /* traditional unix root user */
putSystemId(1000, "system"); /* system server */
putSystemId(1001, "radio"); /* telephony subsystem, RIL */
putSystemId(1002, "bluetooth"); /* bluetooth subsystem */
putSystemId(1003, "graphics"); /* graphics devices */
putSystemId(1004, "input"); /* input devices */
putSystemId(1005, "audio"); /* audio devices */
putSystemId(1006, "camera"); /* camera devices */
putSystemId(1007, "log"); /* log devices */
putSystemId(1008, "compass"); /* compass device */
putSystemId(1009, "mount"); /* mountd socket */
putSystemId(1010, "wifi"); /* wifi subsystem */
putSystemId(1011, "adb"); /* android debug bridge (adbd) */
putSystemId(1012, "install"); /* group for installing packages */
putSystemId(1013, "media"); /* mediaserver process */
putSystemId(1014, "dhcp"); /* dhcp client */
putSystemId(1015, "sdcard_rw"); /* external storage write access */
putSystemId(1016, "vpn"); /* vpn system */
putSystemId(1017, "keystore"); /* keystore subsystem */
putSystemId(1018, "usb"); /* USB devices */
putSystemId(1019, "drm"); /* DRM server */
putSystemId(1020, "mdnsr"); /* MulticastDNSResponder (service discovery) */
putSystemId(1021, "gps"); /* GPS daemon */
// 1022 is deprecated and not used.
putSystemId(1023, "media_rw"); /* internal media storage write access */
putSystemId(1024, "mtp"); /* MTP USB driver access */
// 1025 is deprecated and not used.
putSystemId(1026, "drmrpc"); /* group for drm rpc */
putSystemId(1027, "nfc"); /* nfc subsystem */
putSystemId(1028, "sdcard_r"); /* external storage read access */
putSystemId(1029, "clat"); /* clat part of nat464 */
putSystemId(1030, "loop_radio"); /* loop radio devices */
putSystemId(1031, "mediadrm"); /* MediaDrm plugins */
putSystemId(1032, "package_info"); /* access to installed package details */
putSystemId(1033, "sdcard_pics"); /* external storage photos access */
putSystemId(1034, "sdcard_av"); /* external storage audio/video access */
putSystemId(1035, "sdcard_all"); /* access all users external storage */
putSystemId(1036, "logd"); /* log daemon */
putSystemId(1037, "shared_relro"); /* creator of shared GNU RELRO files */
putSystemId(1038, "dbus"); /* dbus-daemon IPC broker process */
putSystemId(1039, "tlsdate"); /* tlsdate unprivileged user */
putSystemId(1040, "mediaex"); /* mediaextractor process */
putSystemId(1041, "audioserver"); /* audioserver process */
putSystemId(1042, "metrics_coll"); /* metrics_collector process */
putSystemId(1043, "metricsd"); /* metricsd process */
putSystemId(1044, "webserv"); /* webservd process */
putSystemId(1045, "debuggerd"); /* debuggerd unprivileged user */
putSystemId(1046, "mediacodec"); /* mediacodec process */
putSystemId(1047, "cameraserver"); /* cameraserver process */
putSystemId(1048, "firewall"); /* firewalld process */
putSystemId(1049, "trunks"); /* trunksd process (TPM daemon) */
putSystemId(1050, "nvram"); /* Access-controlled NVRAM */
putSystemId(1051, "dns"); /* DNS resolution daemon (system: netd) */
putSystemId(1052, "dns_tether"); /* DNS resolution daemon (tether: dnsmasq) */
putSystemId(1053, "webview_zygote"); /* WebView zygote process */
putSystemId(1054, "vehicle_network"); /* Vehicle network service */
putSystemId(1055, "media_audio"); /* GID for audio files on internal media storage */
putSystemId(1056, "media_video"); /* GID for video files on internal media storage */
putSystemId(1057, "media_image"); /* GID for image files on internal media storage */
putSystemId(2000, "shell"); /* adb and debug shell user */
putSystemId(2001, "cache"); /* cache access */
putSystemId(2002, "diag"); /* access to diagnostic resources */
/* The range 2900-2999 is reserved for OEMs */
// The 3000 series are intended for use as supplemental group id's only. They indicate
// special Android capabilities that the kernel is aware of.
putSystemId(3001, "net_bt_admin"); /* bluetooth: get any socket */
putSystemId(3002, "net_bt"); /* bluetooth: get sco, rfcomm or l2cap sockets */
putSystemId(3003, "inet"); /* can get AF_INET and AF_INET6 sockets */
putSystemId(3004, "net_raw"); /* can get raw INET sockets */
putSystemId(3005, "net_admin"); /* can configure interfaces and routing tables. */
putSystemId(3006, "net_bw_stats"); /* read bandwidth statistics */
putSystemId(3007, "net_bw_acct"); /* change bandwidth statistics accounting */
putSystemId(3008, "net_bt_stack"); /* bluetooth: access config files */
putSystemId(3009, "readproc"); /* Allow /proc read access */
putSystemId(3010, "wakelock"); /* Allow system wakelock read/write access */
/* The range 5000-5999 is also reserved for OEMs. */
putSystemId(9997, "everybody"); /* shared between all apps in the same profile */
putSystemId(9998, "misc"); /* access to misc storage */
putSystemId(9999, "nobody");
}
private static void putSystemId(int id, String name) {
// Check if the uid exists before adding it so we don't add unsupported ids.
if (android.os.Process.getUidForName(name) != id) {
// Not valid on this system. Most likely due to a lower API.
return;
}
SYSTEM_IDS.put(id, name);
}
/**
* @return An array of system UIDs
*/
public static SparseArray<String> getSystemIds() {
return SYSTEM_IDS;
}
/**
* Returns the UID/GID name assigned to a particular id, or {@code null} if there is none.
*
* @param id
* The UID/GID of a process or file
* @return the name of the UID/GID or {@code null} if the id is unrecognized.
*/
public static String getNameForId(int id) {
String name = SYSTEM_IDS.get(id);
if (name == null) {
if (id >= AID_SHARED_GID_START && id <= AID_SHARED_GID_END) {
name = String.format(Locale.ENGLISH, "all_a%d", id - AID_SHARED_GID_START);
} else {
int appId = id - AID_APP;
int userId = 0;
// loop until we get the correct user id.
// 100000 is the offset for each user.
while (appId > AID_USER) {
appId -= AID_USER;
userId++;
}
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
// u{user_id}_a{app_id} is used on API 17+ for multiple user account support.
name = String.format(Locale.ENGLISH, "u%d_a%d", userId, appId);
} else {
// app_{app_id} is used below API 17.
name = String.format(Locale.ENGLISH, "app_%d", appId);
}
}
}
return name;
}
private AndroidFilesystemConfig() {
throw new AssertionError("no instances");
}
}
Using Reflection:
Inspired by odexide's answer, here is some really ugly reflection I wouldn't advise using that will get the UID/GID name from getpwuid(uid_t):
public static String getNameForUid(int id) {
try {
Class<?> clazz = Class.forName("libcore.io.Libcore");
Field field = clazz.getDeclaredField("os");
if (!field.isAccessible()) {
field.setAccessible(true);
}
Object os = field.get(null);
if (os != null) {
Method getpwuid = os.getClass().getMethod("getpwuid", int.class);
if (getpwuid != null) {
if (!getpwuid.isAccessible()) {
getpwuid.setAccessible(true);
}
Object passwd = getpwuid.invoke(os, id);
if (passwd != null) {
Field pw_name = passwd.getClass().getDeclaredField("pw_name");
if (!pw_name.isAccessible()) {
pw_name.setAccessible(true);
}
return (String) pw_name.get(passwd);
}
}
}
} catch (Exception ignored) {
}
return null;
}
回答2:
The UIDs are hardcoded for the android implemention of libc (bionic) and also are provided in ranges for apps. android_filesystem_config.h explains the mapping.
You should be able to use the bionic stubs (c++) for getpwuid(uid_t).
For more info on the stubs, see this AOSP documentation.
来源：https://stackoverflow.com/questions/23454000/how-to-get-username-using-uid-on-android